I'm curious how will this work with nested packages, i.e. a package inside a __pypackages__ dir can easily have its own __pypackages__ and so on.

Could that be a solution for avoiding version clashes when specifying dependencies? Right now, installing all the requirements on a legacy system I have inherited gives me the following notification:

    package-xyz has requirement six==1.10.0, but you'll have six 1.12.0 which is incompatible.

With __pypackages__ it might be possible to install six 1.10.0 into package_xyz/pypackages, and six 1.12.0 globally...