As I write this, we're now about one week into the Crystal Cleanse realm event. So how well are we doing, are we going to make the one billion crystal maximum milestone, and are there any other interesting bits of information hiding in the crystal data? Well let's start with this: here's our crystal opening efforts, in chart form:

Our crystal openings are in blue, and for comparison the orange line is the average rate necessary to get to one billion, if we averaged the same rate throughout the event. [Note: the x-axis for all charts in this post represent hours since the event started] As you can see, we are currently well above the pace necessary. However, we are also losing ground relative to the pace line. If we focus on just the last five days (the first two days were extraordinary, which you'll see in a moment) out to the end of the event, it looks like this:

And if we extrapolate to the end of the event, we get something like this:

Assuming we hold our current rates (and we could slow down more over time) we're currently projected to land somewhere around 800 million crystals, plus or minus. Now, two different factors can change this. First, in general I would expect our average crystal opening rate to decline even further, as players run out of stashes of crystals. But as we saw with Road to the Crypt, I would also expect there are batches of players waiting to closer to the end of the event to pop open a lot of crystals. Are there enough such players to make up a 200 million gap? I would suspect not, but it is possible.
Another way to look at our crystal opening activity is to look at the rate of crystal openings rather than the cumulative total number of crystals. I'm limited by the number of data points I have collected (I'm just trying to remember to capture data points occasionally throughout the day, and I'm only collecting data points in the middle of the night if I happen to be awake for some work purpose) but I think I have enough data to give a reasonable picture of this:

The blue is our average crystal opening rate per hour in between data points collected. So if I collected one data point at 9am and another at 10am, I assume the average opening rate is the difference in crystals between those two times divided by an hour. We started off at over 13.4 million crystals per hour. That is over 3700 crystals
per second. Different crystals take differing amounts of time per crystal to open, but it is extremely difficult for a single player to sustain an opening rate of over 3-4 crystals per second popping ten at a time. So we're looking at over a thousand players at a time popping open crystals at our peak opening moments right out of the gate.
Making some reasonable guesses about crystal opening activity, I would guess that the first day of crystal openings represented the efforts of about fifty to a hundred thousand unique players/accounts.
Now the orange line represents the average opening rate we would have to sustain
from that point to reach one billion. It looks like a straight line, but that's because it is zoomed out a lot due to the very high opening rates on day one. If we look at that same graph but eliminate the first two days, we get this:

Again, the blue line is our average opening rate, and the orange line is what our required rate would be at that point. It isn't a straight line, because whenever our rate is above the line the required rate in the future drops (because we are getting ahead of the requirement), and when our rate is below the line the required line in the future rises (because we are falling behind).
One of the things I was wondering was would we get a weekend bounce, like we did with RttC. In RttC we saw increases in death counts because presumably there were many people saving Necro runs to the weekend where they had more time. And we kind of see a bit of a Saturday morning/day bounce, but not really much of a Sunday bounce. Overall, I would say the data currently shows that while players might save hard content for the weekend, they are less likely to save something like crystal openings for the weekend, and there aren't all that many players that only play on the weekends, at least not many that are sitting on large crystal stashes they wish to part with.
There is a very consistent activity cycle where crystal openings are much higher during the period from about 11am Pacific to a few hours later. It is lowest in the evenings Pacific time. That would make sense on the first day, since that was when the event started, but that pattern persists throughout the week. Interestingly, mid-day Pacific time seems to be when crystal opening activity is the highest. That doesn't mean that is when players are most active. It could be the opposite: that is when many players are not doing content, so that's when they are opening crystals (when crystal opening rates are highest, players have to be logged in but they can't be actually playing content for obvious reasons).
It will be interesting to see how the second week shakes out, and how the entire event unfolds. Does the crystal opening rates continue to slowly decline? Do bursts of new players show up in the data, or alternatively new stockpiles of crystals? Will we see more players decide to part with crystals if they see us fall behind the pace (at the moment if you're only looking at milestone data, it can seem like we have all the time in the world to reach a billion since we've reached quite a few milestones in just a few days)? Will there be a collective desire to push in the last week? We'll see.