I've read this entire thread. My gut instinct was that obscuring the dungeon progress from players was the best solution because I don't like the idea of people being rewarded for being lazy (the fishers).

Now I've had time to read both sides, I agree that separating the queues is the best solution.

Say 100 lazy people queue for in progress, that's 100 people that need to leave a dungeon in progress before all of them get a spot. This is going to be way longer than completing a dungeon from start to finish.

Eventually there will reach an equilibrium between waiting specifically for a dungeon in progress and finishing a dungeon from start to finish. Certain people will prefer one or the other.