I actually wonder what sort of "addon" content they will be releasing. Changing the interface and stuff would be great though (more options is always great).

However I doubt we will ever see officially endorsed addons, made by users for the game considering they have the power to change the user experience for some (PC players) and make it easier for them to play the game and the PS3/PS4 players would be at a disadvantage (Unless you could put them on those versions too which I doubt)

I doubt we'll ever see an addon culture kinda like other MMOs have (I'm looking at WoW as a big example) because of the console players and I fully understand and support the developers in that decision.