The PEP process is straightforward. However, a PEP may produce an outcome that proves after more experience to be wrong. ISTM a prerequisite to choosing a DVCS is that it should support the full range of development platforms and thus the PEP was accepted prematurely.
To be as blunt as possible: the PEP was accepted because Guido really, Really, REALLY wanted to switch to Mercurial. So you would have to convince Guido to revert his decision. You may not like the decision (I did not like using a DVCS in the first place), but following such decisions has served us well, and will serve us well this time.
At some point the PEP should be reexamined and, if necessary, rescinded. What I don't understand is why the plan is still to move to hg despite, after several months, there not being a known good way to include Windows eol support.
You don't understand why it takes many months? That's also easy: because there is a single volunteer, and because there is a lot of work. I think it took me a year to migrate to subversion back then, and I wouldn't be surprised if the Mercurial migration takes even longer.
Or don't you understand why that single unresolved item didn't manage to revert the decision? Well, there are many unresolved items in the Mercurial conversion, some much more stressful than the eol issue (e.g. the branching discussion). None of them is unsolvable (AFAICT); you can either contribute to the solution, and sit back and wait for solutions to emerge. Then you can vote on PEP 385 up or down still.