I did this with regular tessellation back in the day, so it should work in theory: Seamless Terrain/Mesh blending - it's alive!!! - Album on Imgur
However, whenever I played with it and nanite, I always got those hard edges, staccato-triangles like you seem to be getting. I gather it was somehow related to the way I generated my heightmaps/displacement-maps and/or the settings I was using.
For nanite: I could never make it work-well enough, but I still don’t know if that was me or the tech.
Reminder: WPO maths on nanite are run Thrice (3x), so the pass is the same cost, but it’s run more than once… Plus, nanite tends to have more vertices to run that pass across so that’s a nice double-ding…