They can identify if the account is being leveled by a bot and they actually try to put those bots into “bot only” Co-op vs. AI queues. There was a whole dev post about it. So it wouldn’t be that hard to do something when a bot-leveled account suddenly queues into ranked.

As for what that “something” is, I agree that it’s not clear. I’m just spitballing here, but maybe they could factor the bot-leveled account’s performance into the ranked MMR calculations. So, if that account crushes its first placement match, it’s second match would be at a much higher MMR than a normally leveled account in the same position would be. That would at least minimize the amount of games that smurfs spend at silver and gold elo.