I think it would help discussing your options if the patch passes test_buffer
first.  Currently it segfaults because shape can be NULL.  Also, code in
memoryobject.c relies on the fact that ndim==0 means contiguous.

Then, it would help enormously if you give Python function definitions of
the revised C and F-contiguity.

I mean something like verify_structure() from Lib/test/test_buffer.py -- that
function definition was largely supplied by Pauli Virtanen, but I may have
added the check for strides-is-multiple-of-itemsize (which 2**63-1 usually
isn't, so the new debug numpy strides don't pass that test).