The best from Skyrim to morrowind

[bahamut]

A higher poly terrain mesh wouldn't be very useful without a landmass overhaul mod. The mesh density will have to remain that of the data files, unless you perform some fancy interpolation.

Use procedural generation (fBm,noise) to add a bit 'salt' to the current landmass. This would generate a higher poly terrain mesh based on existing landmass.

This. I'm also pretty sure Vality7 had some better quality heightmaps (or at least has the tools/knowledge to make some) for Vvanderfell.

If you talking about some mountains he showed once, these where meshes

[SquireNed]

A little off topic, but I do like to salt the earth. Pun/lame word choice aside, the one problem is that it could pick up some iffy object placement. I don't think we'd see a significant performance impact, however (at least if the mesh data is stored and not like rebuilt each frame or anything).

[Mistahtokyo]

A higher poly terrain mesh wouldn't be very useful without a landmass overhaul mod. The mesh density will have to remain that of the data files, unless you perform some fancy interpolation.

Use procedural generation (fBm,noise) to add a bit 'salt' to the current landmass. This would generate a higher poly terrain mesh based on existing landmass.

This. I'm also pretty sure Vality7 had some better quality heightmaps (or at least has the tools/knowledge to make some) for Vvanderfell.

If you talking about some mountains he showed once, these where meshes

No, I meant heightmaps.