I've just released #pycargoebuild 0.8 and pushed it to #Gentoo.
The killer feature in this version is support for GIT_CRATES. Please test and let me know how it works for you (yeah, I know you can't because of workspace package data, sigh, that's coming up next).
It took some effort but it can guess the fancy paths for GIT_CRATES, remove the variable if it's stale or add one if it's missing.
@mgorny Oh, that can update existing ebuilds! That should be helpful!