PyMem_GetAllocator() and PyMem_SetAllocator() have a domain parameter which can take 3 values: PYMEM_DOMAIN_RAW, PYMEM_DOMAIN_MEM and PYMEM_DOMAIN_OBJ.
I don't think that we need 3 flavors of allocators (PyMem_Raw, PyMem, PyObject).
Maybe the PYMEM_DOMAIN_RAW domain is enough: OS functions don't require the GIL. In this case, should we add a new pair of Get/Set functions with an associated structure? Or maybe PyMem_SetAllocator() may ignore the aligned members of the patched PyMemAllocatorEx structure for domains other than PYMEM_DOMAIN_RAW? And PyMem_GetAllocator() would fill members with NULL.