Also - I have a strange feeling they're going to do a content patch at some point which opens the Necromancer as a companion as well. I can feel it.
I'd guess more like the next expansion, which was setup fairly obviously, imo. The Scoundrel quest
ends on a cliffhanger and almost flat out tells you there will be more to do
that guard in Westmarch
I mean, there might be an alternate universe where Blizzard looks at its 3+ million copies of Reaper of Souls sold x $40 and goes "nah, we don't need to do another", but I doubt it.