It's also not ready yet, missing critical features like editable installs. Right now, you still need a shim setup.py. Until pyproject.toml can actually replace setupy.py, I see little incentive to start using it: It's just one more file to add. The one exception is if the package actually has build requirements, e.g. for Cython modules.
The only reason we use pyproject.toml is because of the stupid black formatter that refuses to support setup.cfg, which every other python tool under the sun supports.
There are other formatters, some may even be better.
Yeah, it's annoying. But Black has so little configuration that I'm ok with hardcoding command-line parameters in my Makefile/tox.ini/precommit hooks (`--skip-string-normalization --line-length 79`)
I don't recognize this. I use poetry all the time, without setup.py and the local installs are editable. I have published half a dozen packages which don't have a setup.py and they all work fine.
You can't install a poetry package editably into another environment. It's really a missing feature in the pyproject spec. There's an open issue about it under one of the pypa repos. Someone just needs to do the work of implementing it in pip/setuptools.