It might be too early to mention that, but right now the terrain looks repetitive at places where there's a lot of one type of it.
In KaM, we first picked a brush (for example, grass brush), painted all over the grass areas, then picked individual tiles (which looked almost the same as the main, clean grass tile, but they were slightly different) and made the grass more varied with it.
I assume that's not the way you'd want it to be in KP. I am not sure you want to let people use tiles at all (I think that instead, you're opting for simple textures), but how about somehow randomizing the textures, or having 4-5 texture sub-types of most of the terrain variants? The way I see it, a sub-type would be just another brush, but just like KaM individual tiles, it could be used to subtly change the terrain appearance. I think these sub-types would definitely be needed for grass and any other frequently used types, like dirt. On a second thought, though, for the final game it would be ideal to have it for stuff like mountains as well - I'm not sure whether you're familiar with the procedure of making good looking mountains in KaM (using individual tiles and elevating them properly to make nicely looking cracks etc.), but something similar might be needed for KP too - so, some cracked mountain textures might be nice as well.
If there's any more explaining needed, simply catch me on TS or ask for more details here, I may try to make some screens to clarify what I mean.
By the way, a random question: will mountains cast shadows?
edit - any plans for animating the textures, for example for lava?