well the mainland has an east
actually we have been there once before for the tribunal questline.
i hope for morrowind, but not vvardenfell. mainland would have alot of argonian influence, which is a plus

Mainland has an east, certainly, but east mainland is not east Vvardenfell. Thus it wouldn't necessarily have the vampire infestation that east Vvardenfell is known for.
As far as what I would like to see from Dawnguard:
-Everything I've heard rumored thus far seems fine. Potential storylines involving Falmer and vampires is fine by me. My character would actually thrive greatly in a vampire focused story arc as well. Crossbows, while I don't want them persay, any additional weapon options are always welcome. I don't care about water combat, but again, anytime you're
adding options, I won't complain.
I'd like:
-Spell combos like seen in the GameJam.
-Additional spell effects, notably many of the removed ones like Summon spells, Bound spells, and Command spells.
-New locations - Tribunal and Bloodmoon were completely different areas away from Vvardenfell, Shivering Isles was an entirely new area away from Cyrodiil, I would like new areas that aren't Skyrim's mainlain. Whether that goes into Hammerfell, High Rock, Morrowind, or some other area, I want a non-Skyrim area we can go to. I'm sure this won't be a problem.
-I mentioned GameJam spell combos, in all honesty, I'd like to see many of the things seen in that video, though not necessarily everything. But notably, Spell combos, house building, spears (only because it is more options, not because I think the game is suffering for a lack of spears), enemies relighting areas, the dungeon enhancements, follower favorites, adoption, mounted combat, graphics upgrades... the only thing from the GameJam I really wouldn't want would be the skeleton butler and the giant mudcrab.
-New factions would be cool too.