> it uses pyproject.toml which is what Poetry uses and seems to be the standard people are moving to
Yes, PEP 517 is standard now. But, that's not actually a build system and depending on how you configure it, the actual contents can differ wildly. While build-system.build-backend is standard, how one actually configures that backend in tools.<your-build-tool> are not standard at all.
It's more proper to think of it as a standard meta-format for build system configuration.
There is effectively no real portability between build/project tools except in the most absolutely trivial cases.
#1987 is actually outdated and way too small. Nowadays it should include build/install/pip/flit/rye/setup/setuptools/setuptools-deprecated/poetry/[insert 50 more build tools].
Probably not actually a large issue here since it uses pyproject.toml which is what Poetry uses and seems to be the standard people are moving to.