To clarify, the additional mercs and ability to switch between the type you had out is not a feature tied to the expansion release itself. It is a feature the devs are reportedly working on, to be implemented in game with a patch at a future date. I'm probably optimistic, but I'm hoping it drops in a December patch. That is one of the game feature updates I am very eagerly looking forward to, probably second in my priorities to the awesome new hotbars in the UI, which *IS* an expansion release feature.