Short answer: everyone promotes easier. Weaker players promote further. GC-caliber players will take fewer matches to reach GC.
I've done a few analyses of promotion in VT. I'm linking them here for reference, for those who want an explanation of the math, which I'm not going to go into deeply here.
Battlegrounds math: how hard is it to progress through the Victory TrackAnalyzing the Battlegrounds Medal Change (TL;DR: Its Good: Very Good)Given a particular average win percentage for a player, it is possible to calculate the average number of matches they would have to play in order to promote to a particular VT tier, given how many medals it takes to promote. For reference, this is a table of matches to promote for S18, the last season played to date:

So if you're, say, a player that typically wins at about a 60% rate, it'll take you about 8.3 matches on average to promote to Platinum 3 from Gold 1 (yeah I know the column says 59%, that's a long story, its close enough for our purposes). The table also shows some interesting subtotals. If you are a GC-caliber player, your season reset is to Platinum 1. From Platinum 1, it takes on average about 84.8 matches to reach GC again ("Total to GC from GC seed"). If you took a season off and started over, it would take you 146.5 matches ag that 60% (ne 59%) win rate to go from Bronze 1 all the way up to GC.
Of course, players do not have consistent win rates. They tend to win at a higher rate early when they are facing weaker competition, and then win at a lower rate when they "catch up" to stronger competition. These numbers do not predict how many matches a player will take to reach GC, because no player has the same win rate from Bronze to Vibranium. However, these numbers are useful to predict single tier VT promotions, where player win rate tends to be less variable overall, and more importantly they can be used to compare what BG looks like now with what it will look like with the two Victory Track changes that have been announced. First, players will get two medals for every win, all the way up to GC. At the moment this only happens up to Gold 1. And second, Kabam just released the new medal structure for VT in their latest live stream. Here is what that same table above looks like for the Victory Track for season 19:

Let's focus on just the subtotals for a moment. For a given player of a certain win percentage rate, how many matches to reach GC from Bronze, how many matches to reach GC from the GC seeding position, and how many matches to reach that seeding position starting from Bronze:

First, let's look at "Total to GC from GC seed." We can see that for every win percentage, S19's number is
lower than the S18 number. In other words, for all players in GC now, their climb back to GC from the seeding position they will have will be shorter.
[Note: In S18 players seeded six tiers lower than their previous season finish but with a ceiling of P1. In S19 players will seed eight tiers lower but with a ceiling of D5. So the GC seeding position for S19 is Diamond 5, not Platinum 1]
Yes, I know,
this contradicts what was said on stream. The *intent* was for the changes to make it easier for weaker players at the expense of making it slightly harder (take longer) for stronger high win percentage players. However, that's NOT what the announced numbers do. They actually contain slightly fewer medals required than would be necessary to do that. This was a change in intent as the numbers evolved, that was not reflected on the stream. As John (Kabam Crashed) stated on-stream, I did some work with Kabam to refine these numbers to properly match the intent they were going after, and the calculations I'm showing here match their own internal balance calculations (or rather are close enough to be essentially in agreement). While I am giving my own personal narrative explanation of these numbers, these numbers are for all intents and purposes the same as Kabam's design numbers. They see the same things I see.
Next, let's look at how long it takes to get from the start to the GC seed. This is an interesting landmark, as it sort of measures the "start up effort" for a player. If you are a GC caliber player (someone capable of consistently reaching GC) but are starting now, that's initial effort you have to do at least once. Once you reach GC, you will never have to do that again because your season starting seed position will always be above those VT tiers. Conversely, if you are not a GC caliber player, then this is the region of VT you'll likely be repeating at least a part of in every season, as your VT seeding start position will be lower than the GC seed (technically, anyone who reaches V2 or higher seeds here: there is a seeding "ceiling" that no one can start a season higher than, which is where GC players automatically go to at the start of a new season). We can see that for some players, this march up the lower VT tiers is shorter than it was in S18. From 55% and lower, the number of matches to progress through the lower tiers is smaller in S19 than S18. But from 59% and higher, the number of matches to progress through the lower tiers is somewhat higher.
So, if you are a weaker player that wins at lower percentage rates, the climb through VT will be easier - it will take fewer matches to climb to higher tiers, up to a point. If you are a stronger player with a high win percentage rate, your climb through the lower tiers will now take more matches. However, if you are a stronger player with a high win percentage rate, you probably won't actually *be* climbing through those lower VT tiers often if ever. So this is less of a real problem for those players, unless they take a season off and reset to zero.
So if you are a player that regularly makes it to GC, your climb back to GC is going to take fewer matches. There's some good and bad to that: on the one hand less of a grind to get back to GC, but on the other hand fewer matches means less solo milestone points during the VT climb, so you'll have to earn more of your solo points in GC instead. If you are not such a player then most likely you will be doing fewer matches to climb to higher tiers in VT. The higher your win percentage, the greater the chance that your climb through lower VT tiers will take longer, but also the greater the chance that you won't be doing that often if ever.
Those are the big picture numbers. But what will it look like for players actually trying to win matches and actually promote in VT, tier by tier? If there's one thing I think that will jump out at people at a glance, it is that there are
a lot more VT tiers. S18 had 19 tiers, S19 is going to have 30. But more tiers is not necessarily bad, if they get easier. Let's pretend I replaced Vibranium 2 with two new tiers, V2a and V2b, and each of those new tiers took three medals to promote in. I've doubled the tiers from one to two. I've increased the medals from five to six. But have I made it harder or easier? For the vast majority of players, easier. It takes a lot of effort to promote in a tier that requires five medals. At any time a losing streak can reset you all the way back to zero. But it takes a lot less effort to promote in a tier that requires three medals. And when you break up one tier that requires five into two tiers that require three, you sort of create a "save point" in the middle of that tier. Once you promote from V3 to V2a, you can never slip back down. Those three medals you earned going from V3 to V2a can never be lost. All you have to do now is win three more to get to V2b.
More tiers, more medals, but *easier* promotion. And that's what's happening in the new VT. There are a lot more tiers, but they have all gotten way easier to promote in. Bronze used to take three medals to promote. At 2 medals per win, it still took two wins. Now in S19 Bronze takes only two medals to promote, which means it only takes one win. In fact, in Bronze losses cost you nothing, because you can only have zero medals or two, and two is enough to promote. You will be promoting in Bronze
on every single win. That's true all the way up to Silver 3. Silver 3 through Silver 1 is essentially identical to S18, because it requires the same number of medals (3) and you win the same number of medals per win (2). There are now five Gold tiers but they only take three or four medals to promote in, instead of the five medals it took in S18.
For example, in S18, a 50% win percentage player would take on average eight matches to promote through each of the three Gold tiers. In S19 there are five Gold tiers, but they take only 4.7 to 5.6 matches to promote. So more tiers, but each tier is easier to promote. Overall it will take more matches, but because each tier takes less effort to promote out of, players will tend to stall less often, and they will tend to be able to go higher overall.
Another way to look at it is that we often say that every player has a ceiling: the point at which they aren't going to be able to go any higher. That's not technically true, no player, however bad, has a mathematical ceiling, because there is always a *chance* however small that they could promote with enough matches. But there is a practical ceiling. If it is going to take a thousand matches to promote, effectively that player is stalled. How many matches it takes to promote is a measure of how difficult it is to promote, and when that number gets too high, the player is stuck. By changing VT so there are more tiers, but each one is easier to promote out of, the "ceiling" of each player has moved upward. It might take more matches, but they can promote to higher tiers without hitting a wall. And as the tables show, the number of matches to promote out of a tier is always lower in S19 than S18 (except for the corner case of Silver3-1, where it is equal).
To summarize:
If you are a GC-caliber player, it will take less effort for you to climb back to GC in successive seasons.
If you are a weaker player that is having trouble promoting, then for the most part you will climb higher and do so faster. You may not necessarily get to GC, but you will almost certainly get higher than before, and usually with fewer matches played. The break even point is in the high 50s percent win rate. Below that, you'll take fewer matches to promote higher. Above that, it will still be easier to promote but it will take more matches overall to promote through the bottom half of VT. Keep in mind that most players who had a significantly higher than 50% win rate were not "weaker players having trouble promoting" they were tending to reach high VT or GC, and would not be suffering through promoting through the lower ranks of VT every season.
And finally,
for essentially all players, for any given VT tier it will take fewer matches to promote. For weaker players, the combination of fewer matches to promote and more tiers to promote through will end up requiring fewer matches overall. For stronger players that win at higher rates, this will mean more matches to climb out of the lower tiers, but they will likely only have to do that infrequently, as their starting seed position will skip over most of those tiers. Overall, most players, and especially the weaker players, will have a higher ceiling in S19 than in S18. Many players who could not previously reach GC will likely be doing so in S19.