Merging, Transitioning, or Blending from one texture to the other based upon Height Maps

I've created a whole lot of wall textures attached to quads (each currently has their own material) but I want them to blend seamlessly instead of meeting at a vertical or horizontal line.

My first thought was to use the heightmap information, fade each heightmap to black in the opposite direction, then overlap the 2 heightmaps and compare them, with the highest points 'winning' and appearing visible, while the lowest points for each pixel losing out and not being shown.

This way the two bumpy surfaces will appear to merge naturally.

I figure this can either be done at runtime with a shader, or I can precompute and save the various outputs.

What I did not want to do is all combinations manually as the more textures I have, the more exponential the combinations become (even restricted to 2 horizontal and 2 vertical transitions).

I've done quite a bit of searching but have unfortunately not come up with anything thus far. I'll create a mockup tonight of what I'm trying to achieve, but any assistance (however small) would be amazing.