Never heard of Roscrea before either, Atmora i have but the nords left that area what could be done there
I think some Nords stayed behind in Atmora while the others traveled and established the kingdom of Skyrim. I think it would be kind of cool to see how these Nords that stayed behind have changed since then. It's thousands and thousands of years we're talking about.
Atmora is the original homeland of all of mankind, since the Nords were the first of mer. That kind of has a powerful ring to it I think.
I imagine Atmora to have expansive cities and caverns beneath the icy surface, with monsters so ancient and big than one could ever imagine. Lots of secrets that have been forgotten a long long time ago.
I think Atmora could be cool, but maybe that's just me