Yea, probably using black and white texture to do the blending. Basically have the shader take the two (?) ground textures and the b&w blending texture and combine them in the pixel shader. This also means the shader itself is reuseable for any material/tile.
However, im also considering using a RGB blending texture, at least if theres need to blend "three ways". I recall that there are some tiles that require this, i believe, but fortunately i think these are few and far between.
This still WIP and ill be trying out stuff and learning, but its looking good.