Blacklists should be dropped before they are being introduced
This is clearly a pro - whale move. Imagine not being able to use a champ for entire month. Whales can rank up other options easily but ftp/casuals will suffer, especially if, let's say dthanos is blacklisted and he is your only r4(totally possible).
And whitelists, what kind of players can rank up champs just for one season, yes you're right, whales
If they want to make stuff competitive, then implement blacklist/whitelist above mysterium. I don't remember a single soul asking for this and I know it's early to hate something that's not even released, but the cons are too heavy for this one.