> We haven't done RC yet - why is pushing this now so bad?

I reverted your change because it broke all Windows buildbots, and we have a policy to revert a change if buildbots turn red and no fix can be found in 2 hours:
https://pythondev.readthedocs.io/ci.html#revert-on-fail


> Most of the change is purely additive and does not modify the code base, the rest is Windows-only or tests.

nitpicking: Your change modify venv and two tests, it's not purely Windows-only :-) By the way, as I wrote in my email, I would prefer to see the venv+tests change pushed in separated change (and explain why you do these changes).


> I'll add checks for outdated build machines, but there has to be a release of this or it remains untestable, so it'll either be from my branch or from the release branch.

Sorry, I don't know Windows App Store, I don't understand the restriction "there has to be a release of this or it remains untestable". Would you mind to elaborate?

Do you mean that buildbots must upgrade to VS 2017? Can Python 3.6 and 3.7 be compiled without any issue on VS 2017? Maybe send an email to buildbot-status if you want to see more buildbots running VS 2017 rather than VS 2015.

--

There was a small bug in your PR, in PC/launcher.c, fixed by commit 4c49da0cb7434c676d70b9ccf38aca82ac0d64a9 (bpo-35436):

+        if (executable == NULL) {
+            error(RC_NO_MEMORY, L"A memory allocation failed");
+        }