I had an idea for how to include TBC and classic together involving a little bit of instancing and progression saving. what if they instead of releasing TBC servers separately we instead when crossing the dark portal it takes a snapshot of your characters current gear and items from classic and upon emerging from the dark portal you now have a seperate snapshot of your TBC character with its own progression, items and talents saved, and upon returning to Azeroth it would load the old snapshot of your classic character allowing classic progress and TBC progress to exist at the same time. This would also fix the issue with server population that will arrive with different servers. This would probably also have to apply to deadwind pass having its own instanced version for karazhan.
this would work kinda similar to the legend of zelda ocarina of time when link goes from child to adult and vice versa https://www.youtube.com/watch?v=ncRH4u7WSsw
there are of course some issues that would arrive from this method but id love to hear everyone’s thoughts