As a note in favour of the "Allow package nesting to be encoded in names, not just directories" approach, we actually have a similar problem affecting builtin modules: they're currently limited to top-level modules, with no way for the module to indicate that it's actually part of the parent package. Details at https://bugs.python.org/issue1644818 (yes, that's a SourceForge era issue number).

The solutions may not overlap in practice, but they're conceptually related (i.e. outside frozen modules, the package topology is pretty tightly coupled to the underlying filesystem layout)