Have you ever been reached image count limitation in cycles GPU rendering? With TextureReducer, You can replace images to merged one w/o modifying UVmap. Even tilable image can can be part of a large image. because TextureReducer can handle it!.
Regardless you have reached the cycles limit or not, Grid based UV assigning is worth to try. It's so powerful and easy to use.
https://www.youtube.com/watch?v=X7_75vD41cE
In my opinion a great idea, but maby a bit complicated so a video would be great=)
Wow, that looks very impressive, well done and thanks for the upload!