@dstufft had a similar proposal in pypa/warehouse#8254. But this only circles the discussion back to where it began. To be able to expose sdist metadata, sdist metadata needs to be reliable, which means an sdist metadata spec needs to be designed, which means we need to standardise sdist. And that discussion (Sdist idea: specifying static metadata that can be trusted) is stalled, so nothing depending on it can happen.
The proposal in PEP 625 is taking what seemed to take one part in the sdist format (the file name) that needs to happen eventually and is not blocked by anything, and do that first. Sure, what it can achieve can also be achieved in other ways if we get to finish the sdist format discussion and everything that currently gets blocked by it, but after that happens, we are very likely going to introduce that file name change anyway, so getting the name change right now would provide the benefits before the discussions finish (or even progress), without affecting what we can do later on.
What I’ve read from every objection seem to all say “we don’t need to do this now because we can do something else.” But we are not doing that something else now, and this still needs to happen after we do that something else. So why is that other thing relevant? That’s what I don’t get.