Quitting is an issue when you're doing it as soon as you go down by 1-2. I don't have a problem with it if you're down by 4+. Some people are awful to play with, and others are awful to play against. Most people have limited free time, and they don't want to spend it getting slaughtered by people who spend all day figuring out the most glitched builds and ways to score.
Imo, if they implement something like this, it should only be for people who quit in the first period. Also, I think they need to add a vote to concede option. And another thing that could help retain people within a game is an option to change their build mid game instead of being locked into something that's clearly not working.