I think at this point it's clear that they are building up to another Lich King expansion. It's either the next one or the one after that.
What I am wondering is
- How are they gonna do that? Bolvar as the main villain would clearly mean that we're sort of tied to Northrend, cause he resides in Icecrown Citadel.
- Would they revamp Northrend? Put Chromie there to switch back and forth between old and new Northrend?
- Would they come up with completely new zones?
- Maybe an expansion in the Shadowlands, but a whole expansion there? Is there enough variety?