Many current terrain engines in modern games use vertex colors for blending. Vertex colors are used just like the pixel colors in a blendmap. You can use the r,g and b values to blend different textures, just thats it's on a per-vertex level not per-pixel.
In normal practice, because terrains have reasonably high, regular tesselations, this is almost inditinguishable from per-pixel blending. Also, it gives you the ability to pre-compute more complex blending methods, such as height and slope blending. You can additionally use a seperate micro-blender texture to give the fades some per-pixel qualities, to even out and make the fade look more natural.
