To be fair, it's kinda hard for them to find something to do that everyone will (more or less)like.
I would love the expansion raid content to not have a tank n' spank aspect to it, but the outcry from all the players who built tanks would be immense.
I'd love to see some mechanism where the raid boss smacked the living **** out of the support toons (healers/bards/cc/whatever) but those people would be on the forums crying about how unfair it is, and many more would be on the forums complaining about how the newest raid needs *more* casters in order to deal with the damage done by the boss.
I'd like to see a raid boss actually fly/teleport, but again people would point out how this favours casters and ranged toons, and why does turbine hate the melees?
The only thing I can think of that might work, is simply a truly random summoning mechanic.
For example, Lloth could summon elder beholders (I think this would be awesome)/horned devils/pit fiend. Or even a bunch of casters with dispel magic & PWK memmed.
But make it actually random summons, at a random time(not the 'her health is at xxx, prepare for the summons that always happens at this point) as well