Opens the space for other build backends than setuptools. The new build backends (such as poetry/flit) can offer a simplified improved UX (e.g. simple TOML configuration file rather than executed python code). New build backends are not obliged to offer feature parity with setuptools (importantly such as building c-extensions). Therefore they can simplify the packaging experience for the majority of users working on just pure python codebase. You can read about this more anecdotally within my blog post at https://www.bernat.tech/pep-517-518/
I don’t think it’s stalled. GitHub - pfmoore/editables I think is a direction we agreed would be great to go down. However it’s waiting for people willing to integrate that with setuptools/flit as POC, and then we can move to standardise it. I’m currently already working on the build tools and the tox rewrite, so until those roll out I’m sadly not available to work on this.