After digging the question,I'd rather go for a minimal change.

- setting .name to '' for '..'
- let it be known in the doc
- special-casing Path('..').stem (to keep the old behaviour)
- update tests

More could be done, but I don't feel like rewriting too much of it.

A global design change should set a special treatment for '..' as well as '.' 

But I'd rather see small steps being accepted than big ones rejected.