I understand your view but that also doesn’t make much sense to me 
Allow me to express my point in a different way:
Do we think the backends of Flit, Hatch, Poetry, PDM, etc. were created just for fun or because PEP 517 told us we could? No, it was because setuptools was too difficult to contribute to. And consider in that case that is merely improving upon its central and only purpose of building packages. In the case we’re talking about here we’re in a code base of equivalent size with even more complexity and we’re talking about not just adding new features but fundamentally changing what it does/is.
That should be a primary concern.