This shouldn't affect the public ABI, so I don't think it's a blocker for the ABI freeze, but it's a regression that effectively makes PySys_AddWarnOption (and related APIs) unusable, so we should definitely fix it before shipping 3.7.

For now, I've marked the bug as critical, and I'll be aiming to have it fixed before 3.7.0b3 at the end of the month.

For PySys_AddWarnOption and PySys_ResetWarnOptions, my current plan is to adjust them to maintain a singly-linked list of "wchar *" pointers when called prior to _Py_InitializeCore (i.e. when "PyThreadState_GET() == NULL"), while using the existing 3.7.0b2 path when the thread state is available. _Py_InitializeCore will then take care of cleaning up the memory allocations while converting them to Python unicode entries in a Python list object.

_PySys_AddXOption would work similarly (just with a separate list).

For PySys_AddWarnOptionUnicode, I think we need to make it call Py_FatalError for 3.7 when called prior to Py_Initialize, with a recommendation to use PySys_AddWarnOption instead. In 3.8, that API will become useful again, once the public Py_InitializeCore API provides a supported multi-stage startup process that allows unicode objects to be created safely before Py_InitializeMainInterpreter (or whatever we end up calling that API) reads sys.warnoptions and configures the warning subsystem accordingly.