So if dps queues are so long....

[Ryans]

Changing the party make-up will destroy the way the current dungeons are set up and the only dungeons where it would work is new dungeons where they would be made for the set up.

A feature like this would break the game.

Break the already faceroll difficulty of the current dungeons? None of them have strategies that would be easier with 5 people. All they'd have to do is scale the monsters HP to offset another DD.