If this dlc is true then i suppose there will be reasons to this stuff. for example: dragon mounts. If this is true and the solstheim place is true, then i think the dragon mounts might be limited to solstheim not skyrim. Also dragons flying speed is without the player mounting it. so the weight might affect the flight. Also the dwemer ruins could have been hidden in solstheim and were never discovered.
This Dlc is looking pretty good in my head, but is it true? I guess we will have to find out.

Use this thread to discuss the rumored DLC.
http://www.gamesas.com/topic/1417570-18-beta-update-solstheim-dlc-hints-thread-13/