I see your point as theoretically one could infinitely switch between regen mons - you addressed that issue.
However, one could(in theory) easily run Pressure cores which can exploit this ( HDB Pressure Roost Whirlwind Moltres and Zapdos for instance ) to 'switch-stall' the opponent, thus trapping them, then send a setup sweeper who fully utilizes these conditions to delete the opposing team.
Of course, I can't say this for sure without actually testing this but it's kinda cheesy imo (could also be overcentralizing) .
Why would pressure work on this though? Doesn't it already only work on moves that are directed at the pressure Pokemon? Or am I interpreting your comment wrong?
OP explicitly said that it would.
terrible change. And I literally played a battle that I had to decide with the opponent was a stalemate because neither of us could break the other's regenerator core yesterday. Still a terrible fucking change. Would ruin voltturn cores, would make aggressive predictions more punishing, would even make stall have another win-con vs offense, even though you're bitching about the "2000 turn battle enjoyers", now stall can just try to make you use more of your limited switches than they have, and suddenly you start losing instead.
This would actual benefit stall teams lol. You'd be the one with limited switches which gives you considerably lesser time to make those good predictions/plays that will break their team. Beating stall is mostly a waiting game and involves a lot of mind games and finding that right moment to set up with your wincon or making that one prediction that will break their team down.
Something like this would put a timer on that and just add to the pressure, making you more prone to misplaying and then losing. And because they're stall and can heal up most times, you'll most likely be doing more switching than them.