Well.. heroics throughout Lich King... we could basically reach 80th level.. and run most of the heroics somewhat successfully.
As in, in utterly crappy I-Just-Reached-Max-Level-Questing gear, down six or seven bosses and be able to kill trash in almost every heroic up to a boss... giving us a lot of attempts at the boss before trash respawned.
I remember a lot of guild members getting both the normal and heroic achievements, for a lot of dungeons, at the same point.

Looking back to Burning Crusade.. sure Slave Pens was one of the easier heroics.. but just about anything else was basically impossible in the gear you'd have as a fresh 70th.



I'm hoping Cataclysm is closer to BC then WotLK, in terms of difficulty. As in, not doable with fresh to 85th level gear, but doable and challenging with level 85 initial crafted/normal mode 85th dungeon loot.

I'd like to see crowd control as something which makes a fight a lot easier, but not something that is absolutely essential...
I remember quite a few heroics in the BC era; they would need a mage or hunter, with a rogue/warlock as a lesser choice because of humanoid mobs. If you were a Shaman DPS, they would not take you.
I'd like to see pretty much all group compositions be viable - which I define as sufficient to clear the content, even if it takes a lot longer.

Pretty sure they'll all be doable, initially even, given the right classes. Hopefully, they'll all be doable initially, given the wrong classes (assuming a Tanking class and some kind of Healing).
Down the road... that might not even be a requirement.