Wouldn't fix the problem. In response to the extra dps bandwidth more people would ignore all the incentives to play tanks and healers and start DPSing more. We'd end up with queues just as clogged with even fewer tanks and healers in queue. The long DPS queues are partially an incentive to play tank or healer. The moment it's easier to queue dps people will do so recreating the exact problem we are in.

This doesn't address the fundamental problem. Many people do not like playing tanks or healers. The moment they don't have to they won't. That will hurt everyone.