I'm looking forward to Warhammer, but doubt this will do anything for the problem you've stated above. Warhammer will be very much like WoW, in every way. The only difference (which might actually intrigue you) is that WAR was built from the ground up based on PvP, from small skirmishes to medium-sized objective based struggles (scenarios/BGs) to small keep/castle seiges (including Seige Weapons) to all-out city assault. PvP plays a part in how your faction and your own PvE experience will turn out, and vice versa.

Age of Conan has a pretty entertaining idea for PvP mechanics, but the actual mechanics and balance between PvP damage and HP is very badly flawed. As such, there are a lot of changes swinging the balance heavily back and forth, always missing the mark. It's worth a shot I suppose. Only 3 classes are Multiboxable in its current form (imo).

For a change of monotony (I said change of, not change from) you could try the crafting portion of Everquest 2. Try starting on as new a server as possible, and a PvE one at that, as you will find old servers extremely difficult to vie in as a new player.

Maybe MMOs are not going to satisfy you anymore. You could try some of the good old Turn-based strategy games, be it RPG or Sim.

Some good ones that I still play occasionally are:

Civilization 3 + 4
Age of Empires Mythology w/Titans expansion, Age of Empires 3 + expansions
Shining Force 1 + 2 ROMS for Sega Genesis
Final Fantasy Tactics for PSX
Master of Orion 2 (by far the best TB-Strategy game around), Master of Orion 3
Caesar III