I like the warning. I like the crackdown on AFK and leaving (I guess). Simpler way would be just to make it so people who leave consistently just play with other people who leave consistently. Pretty straightforward problem solving.
"Prisoner's Island" concept has been shot down numerous times both from a behavior stand-point and by extension a leaver standpoint. Yes the karmic justice has nice ring to it, but think about it, do you really want that kind of backwards momentum for players in the long run? What incentive will a player have to keep playing instead of just making a new account?
They've talked about maybe creating a "Leaver Island" type of solution. It works better for AFKs than ragers.
But there are some issues. If it's time-based, people will just switch to (or create) an alternate account to evade the penalty. If it's X games with crappy teammates, people can grind them out rapidly in co-op. This penalty can't be evaded as easily.
