Oh sure, the new MMO will definitely be their biggest current project, and D3 is a little bigger than HotS, but probably not by as much as you think. In fact,

Oh sure, the new MMO will definitely be their biggest current project, and D3 is a little bigger than HotS, but probably not by as much as you think. In fact, when you've got a game as big as WoW, making sure that everything you add plays well with all the existing pieces is a mammoth undertaking - it would probably be easier if it was a new game! As you pointed out, these aren't simple 'Here's 4 new areas with some new enemy models expansions, these are major reworkings of large game features. Although I've never worked on an expansion, from all the games I have worked on those kinds of things are definitely not simple.