I think my ideal MMO would be City of Heroes 2 remade with the same engine and combat style as Tera...
Tera is still a "generic" fantasy MMO with reeaaally generic quests... but the combat is the most fun I've had in a while, MMO and non-MMO games combined.
COH mechanics (sidekicking, alignement, etc), lore and customization merged with Tera-like combat would be awesome...