You know what actually might help a little? Two tier Adventurer in Need rewards.

What I am referring to is this;

I play PLD, my wife plays WHM. I Q and almost always get an extra reward for the run, because I am a tank. But, healers are similarly in short supply, and my wife misses out since she's a healer not a tank. She has very little additional incentive to Q as healer unless she's playing with me. I think that in general, the low incentive for healers to run in DF is not helped by the fact that the acute shortage of tanks means that healers never see the additional AiN bonus.

So, let's say that the Adventurer in Need bonus goes 100% to the #1 role in need, and 80% to the 2nd role in need. This might incentivize more healers to run, and might also help reduce Q times a bit.