I would love something like this. I've been stuck in my Plat III -> Plat II promos because of AFKs or Leaves in 2/3 of my promo games. I think I'm on attempt number 7 or something right now. I would love to have a system that is less painful for players who try, and more painful for AFKs and leavers.
One extreme example, had a lux who gave up at 8mins into the game after dying twice. She sold all her items and sat in base complaining about our jungler, until both top lane and jungle gave up and quit too. We were winning bot lane, and had a strong late game comp (Nasus, Amumu, Lux, Ashe, Sejuani support) against a team of glass cannon assassins that weren't going to scale. I looked through Lux's match history, and she does this every 7 games or so (no items, gold plateaus at quitting minute).
It would be pretty easy for Riot to detect this behavior in the play data, and then set something up where teammates that are actually trying to play the game get less of an LP hit, and the AFK gets the extra LP hit. That way there's a pretty strong punishment to stop people from ruining the game for others. This would also make it less painful for the unlucky players that get paired with the AFKs. I get to win 3 regular games in a row to get back up to promos after I have two 4v5s. If I lost 10lp instead of 25lp with a 4v5, then I'd have to win less to try again.
Just really frustrating being at the mercy of other people who don't care. And a system like this would fix the problem.