openbabel uses cmake, which makes it difficult to build the python
extension for multiple python versions
(it can be done by using multiple subdirs to find each version,
but that's a heavy patch to maintain if it's not merged upstream)

But cython now offers a common python3 abi, so the extension can be
tagged abi3 instead of cpython-314.  I think cmake can be configured
to use it.

openbabel is an ideal candidate for this mechanism, since in principle
it doesn't really care which python version it's built against.

It would increase the usefulness of the package, making it available
for all python versions (and could help improve debci testing of client
packages).