I don't think it's a bad idea overall, but I'm not really sure how much legitimate use it would get especially if it bumped up the queue time. The more casual players would probably end up hedging their bets by selecting the A option and hoping they got along okay. Even the A option players would start hedging their bets too if the higher time spent in the queue started to eclipse the time they would save by running only with faster playing team mates.

And, really, it could be a tough fit for players who find themselves somewhere in the middle too. As an example, maybe they're new to tanking but want to try starting to push themselves. If they go A route they'll get crapped on by the hardcore crowd for not being good enough but then they'll be playing above the level of the C route players. Sure you could say that the players they end up with should just be understanding and communicate respectfully.. but if that was an option then we wouldn't need a change to the DF in the first place.