Let's say my team is winning super hard 20 or 30 minutes in.
Someone on the enemy team tries to surrender, but their team votes no. They ragequit out of frustration because they know a comeback is extremely unlikely.
You cannot make a match like that a draw. You'd be taking a win that one team earned by superior play and erasing it because someone on the other team was being a jerk.
You could potentially cancel matches where one or more players never connect at all, either completely nullifying them or giving the full-strength team a fraction of a normal win and the shorthanded team a fraction of a normal loss (in terms of LP/MMR gain), and the absent player a full loss. This is what DOTA2 does.
Offering IP incentives for substituting in ranked matches would easily net a lot of volunteer's for a replacement queue.
I'm really not sure. You'd almost always get thrown into a losing situation where your champ is behind in gold and levels.
Also, if there's no downside (presumably you would be unable to lose LP/MMR), and you get bonus IP, wouldn't people just spam queue those and farm the jungle or something equally useless for the IP?