To have multiple terrain textures in one level so, for example, part of it is a green valley, while another part is snowy hills, like how Skyrim does it.

Quite so. Everyone supports more Texture support, handling flexibility and availability.



Should be user editable/changeable and part of the internal editor Paint Terrain System so that Texture management and painting brushes/tools for spray/paint controls and effects and alike are done through the editor without resort to external complex Texture creation skills involving textures, shaders, scripts and so on.



I have also suggested in another thread Reloaded should have proper Pro type features for in editor Texture/Materials Editor to include a range of all features that could potentially be attached and managed by Textures. Materials index sounds, bump map, shader selection, friction to allow or restrict or affect player/entity movement over various game materials. e.g. slippery ice or oil and so on.



Pro type features like that seems rather perhaps beyond Reloaded but worth mentioning anyway. Cant see how it could be easily done as it may require complex integration with many deep rooted core things from the beginning?

I agree with this. Paint the terrains using multiple textures, then perhaps save that combined image as a single texture, stored in the texture bank.