I could think of Special-Online-Content, like special quests (with awsome rewards), mby even a up and running Dwarfen-Faction.
Steam is the perfect platform for stuff like this...
Atm, most work is layed on getting the servers full, to give the players the expirience that has been intended. (i think) Aswell, as getting the expansion out.
First of all, there needs to be more endgame-content, that is giving longtime motivation. Archievements, and conquerabe NPC-towns are a great step into that direction, imo.