I think people are overestimating abuse potential, as always.
Might be useful after this 4-man premade nonsense goes away "PICK SUPPORT EVEN THOUGH YOU'RE MID OR WE WILL DISBAND & REPORT",
Reports from premades are already counted differently, It's not just that, as things are they can say "go support even though you're mid" and then report you if you don't, just without disbanding, as far as the penalty inflicted by the disband, they all get it too, and there are 4 of them, so they screw themselves x4 as hard.
So this doesn't create the problem of the famed 4 man, it still remains a problem naturally, but it doesn't make it worse.
but people will also do it to punish ppl who pick off meta champs. At one point Annie/Morg/Brand/Fiddle support were all troll picks and you were reported for playing them - if this existed, those players would be auto-punished even though they didn't do anything wrong.
Again, as things stand, they can still report you for these picks in the usual circumstances(when the game is over).
Mind you I kinda wonder what you intend to pick which will cause 4/4 of your teammates to rather take the penalty than play the game with that pick.
Anyway: This doesn't solve all problems, though it helps with some, but it doesn't really create or exacerbate problems either, so it seems like a decent idea.