If you play support you should be allowed only to pick supports and so on.
I would hate this. IMO the meta is already too forced.
The Tech-curious part of me would really enjoy trying to find algorithms to try and detect trolling.
I expect it would be massively expensive to build an algorithm to detect even a small subset of trolling. A small subset of trolling, and the amount of games with legitimate trolling is already small. So it would be really expensive for little impact. Plus, if some ways to troll become detectable, the trolls just find a different way. So all the investment to solve one type of troll is for nothing.
I don't think there is a solution. And if there is, I expect its massively expensive. I'd rather Riot spend that money on new content: games modes, skins, champions, reworks. Heck, even a new game.
Genuinely would enjoy trying to solve it tho.