We don't want to separate people and lock them in dungeons. Less locations - more points of contact.
About merge, as already was stated: Dion server is NOT a catch up server. It is fully independent server which will have it's own legacy. And might even have it's own update path, which will differ from TI.
But at some point, when the server will reach the stage when we feel the merge is needed, we will come to the community and will have a discussion about it.