DPS queues at the moment are pretty long but they do pop. Any other game and it would be literally impossible to get a match to outdated content but this game has systems in place to make sure you can. There are upper level queues that scale folks down to the older dungeons and give XP/tomestone rewards. This system even incents tanks and healers to sign up because they get in much faster.

What is happening right now is new expansion with two dps classes means people are not focusing on that system as much as they were previously. In a month or two I think things will get back to normal. I rejoined about a month before SB launched and never had any problems with the level 50 dungeons and frequently levelled my other DOM classes with the levelling queue.