Square, please make dungeons 5 players.

[Shurrikhan]

Honestly, I don't think upping the party to five in dungeons is the answer. I think splitting the DPS role is. Instead of being 1 tank, 1 healer, and 2 DPS (or 2, 2, 4 in trials and non-alliance raids) it should be 1 tank, 1 healer, 1 melee, and 1 ranged/caster. (and 2, 2, 2, and 2 for trials and the other stuff). I think that would ease up the queue better for 2.x-current content.

How would that not make the issue worse, if anything?...

On topic:

As Zohja said, reducing the bottleneck allows for faster queues; simple as that. That can be done by increasing the proportion of people interested in tanking (and to lesser extent, healing), or by adjusting the compositions to what's there. Personally, I'd just as much like to be able to see 3 DPS and 1 tank or healer comps as 1/3/1 comps in dungeons. Sadly, SE has gone out of their way to ensure that such things are impossible by stripping the game of most CC as of level 50.

To me, the key is compositional scaling. Want to keep 2 healers busy alongside 1 tank and 2 DPS? So be it. There's now more damage. Want to roll tankless? Alright, better be on the ball with CC, kiting, threat swaps, focus targeting, and environmental damage.