So the rumors of a new 5-man dungeon to come sometime before Icecrown, maybe in 3.2 or 3.3, continue to persist. Assuming they're true, I wonder: What would you like to see? I have a few ideas of my own.
How about a Grimtotem dungeon? Let's unmask Magatha once and for all as a Scourge agent. Some quest lines point to the possibility, and it's an excuse to implement a nice Great Masquerade type quest line complete with confrontation in Thunder Bluff. It's topical to Wrath, and it shakes Tauren lore up a bit. It's a perfect idea all around, as far as I'm concerned.
If that idea doesn't tickle your fancy, I have a few more after the break.