Afaics the preview-proposal isn't even accepted yet - and I think we (well, not actually we in the sense that I'm included ;-) are free to change processes so that they serve us better.
I'm convinced that the current process makes it extremely hard to add big changes to Swift, and that it's time to have an alternative.
Btw, what about Function builders - #374 by minuscorp or _modify? Looking at those two, I think we just have to acknowledge that Evolution doesn't work as it used to do...