Current plan says there has to be separate builds per module, as if it is an ABI break. Would be much better if it could be combined into one build. Hopefully necessity triggers some invention here.
There's no way to make it work with the old ABI. Because sizeof(PyObject) is fixed in the old ABI, there's simply no way to attach additional information (e.g. the new cross-thread ref count) to every Python object. The Python ABI (even the "limited" stable ABI) exposes too many implementation details, it's not really possible to make any fundamental changes to the Python interpreter without breaking that ABI.
You could have a single new ABI supporting both no-GIL and with-GIL, but it wouldn't be compatible with the existing stable ABI.
