The limitations that become apparent are environmental. Skyrim is highly focussed, as expected, on the Skyrim environment. Where Oblivion covered various types of environment from swamp/marsh, thick forest, scrub, coastal and mountainous, Skyrim has none of the same.
Tree types are highly limited. Pine, aspen and a couple of others. Same for logs.
Flora, very limited
Rock types, perhaps not so much a concern as a retexture will change them to any environment and rocks arent difficult to mod.
Landscape textures, again not so troublesome, just take a bit of time.
Architecture. Oblivon and Morrowind cant be ported directly so much work to produce similar.
Creatures, time consuming to create and require a certain expertise.
Until these shortcomings are addressed the basic landscape for other lands cant be produced.
As soon as the CK emerges I will, fingers crossed that the CK can handle it, start work on a large heightmap.
I will do what I can, probably starting with the rocks, to reproduce other environments.
As lots of us will require these basic things, it might be an idea that we pool our efforts and make a massive push to produce the basic environment stuff we will all need very early on in our projects.

