My guess is that we'll be able to bring our Guardian forward to D2 so subclass perks and all that will come with them but gear, weapons and such will be gone. It's either going to be something along those lines or they'll make D2 work like an add-on and in the first 5 minutes you'll find white and green gear that is stronger than your King's Fall or ToO gear. I don't really know what the best solution is though.