Hello,
Due to support for subdirectories being in "planned for the future"
state, we first decided to give the UPM ecosystem some more time to mature before we adapt our structure to fit it. What also kept us a bit skeptical is that recursive dependencies (via UPM git urls, not via git submodules) are not yet planned to be supported.
However, we have just recently read about someone using npm's "files"
field in a upm package.json manifest file (in UPM it's still undocumented, though), which could work without any restructuring. We have not yet tested it, but if anyone can confirm this works, we are more than happy to implement official UPM package support this way.
In general: If anyone has any other ideas on how we could avoid a redundant additional UPM-enabled repository with only the Unity-relevant files in it, we are happy to hear your input!
We could add 3.7-upm
and 3.8-beta-upm
branches where all other runtime files are removed, but this still seems somewhat clumsy.