PEP 517 leads to more freedom and I think innovation in how we build Python packages. Given e.g. the discussion in When you kick the packaging hornet's nest on Twitter, the hornets seem to want an opinionated, KISS solution users/devs do want to have a KISS solution, so I think it would be good that, while multiple systems are supported, one is chosen as the recommended system and featured in guides such as https://packaging.python.org/. That means a) favoring one system and b) actually agreeing on one system.
For actually deciding what system that would be, I agree with you it is best to begin with getting some projects to use it. Would it be useful to create an overview comparing the various build systems? I think it may, considering the various topics that touch upon the build systems.