Texture splatting is an insalenly efficient technique on modern hardware, it's basically few texture samples and LERPs per fragment. You could bake a low resolution colour texture based on your splat weights for distance stuff but I'm not convinced it's worth the time, effort and resources for marginal performance gains (if any at all, or even worse perforance!).
I'm painting the terrain in my editor so no procedural stuff. I guess i'll just add more channels then.
As a side not, wouldn't it be better performance wise to use splatting only on chunks closer to the camera and some other technique on farther ones?
Edit: a common technique for texture splatting is to sample low and hi res textures, with the former being used for distant geometry. You then overlay said hi-res texture onto the low res texture for fragments within a set distance from the viewer. You'd need a transition band for this, though, otherwise there'd be a noticble circular band where the low and hi res fragments meet.