If you want a reduction in queue times you have to get more people to play tank classes. The obvious solution to this is to make entry level tanking gear much easier to access. I have all four tanks and it's certainly not a lack of desire to tank that stopped me from tanking early on. It was the fact that an ilvl 329 tank will die in randoms. So I had to run heroics as dps for a long time before I could queue as tank. If tanks have to start out as dps and dps have to start out as dps and healers have to start out as dps then obviously dps will have long queues. Blacksmiths should level off of producing 333 tanking gear for almost every slot. Leatherworkers should level off of 333 leather with dodge on it. There should also be some easily obtainable healing gear. Probably two trinkets with healing procs so that you're giving a boost to healers and not other casters. Giving people the option of tanking/healing at entry level without bogging the group down will enable them to queue as tanks/healers and reduce the queues for dps.
And while you're at it stop putting tanking gear on the first boss of every instance so that tanks won't leave after the first boss everytime their gear doesn't drop. Make tanking gear drop from the last boss so they're forced to stick around. This is a daily occurrence.