I like this idea as well. The only thing is, where could a large landmass be included onto the current map? West of Skyrim is High Rock, east is Morrowind, and south is the Imperial province. All of those provinces have been visited in previous games before. So it would most likely mean returning to an area the games have already gone to. Which wouldn't be too bad, but I'd rather explore new territory.
Unless they added another island north of Skyrim. Or we could go to what remains of Orsinium (if it is still there), and see how the Orcs are doing.
Orsinium has been rebuild but what I gather it is too far away to be attached to the current map, but they could give us access via an underground (dwemer) railroad system (an idea I posted on the first page).
But we haven't actually been to the area east of Skyrim. The game ''morrowind'' only takes place on Vvardenfell which is only the island part. The area directly attached to Skyrim has been talked about a lot in Morrowind as it has different great houses that are in charge there. It would be interesting to visit it as:
A. we have never been there
B. the argonians took control once, an undead army invaded it afterwards and its current predicament is unknown.