The DF itself is pretty strange it doesn't do things in a logical way. Why a dungeon doesn't auto abandon instantly when all party members leave is beyond me. It depends what the dungeon is when it comes to in progress. Some like EXDR dungeons are popular so will fill up quickly when people leave. Sometimes i think people leave a dungeon too easily when one diva Tank decides to leave because the party isn't what they want or somebody doesn't have perfect gear or because they can't hold aggro on their massive pulls and want to blame everyone else. Tanks queue in progress on these dungeons all the time so somebody new will be along in 5 minutes or less but people will usually see the Tank leave and just follow.

I don't think some sort of priority queue would be workable though since it depends on Tanks and Healers being available it would still be like the regular queue in that 90% of the people in it are DPS. It's the same problem in every single game nobody wants to be a damage sponge or keep people alive they want to blow things up and kill enemies.