That already exists, setuptools has supported it for years and years. Nobody uses it though and they prefer to use virtualenv instead. That may be because setuptools itself wasn't that great, or it may be that people just didn't prefer that mechanism for working.

Doing that isn't really much different than a virutal environment though. The only real difference is that in a virtual environment you essentially have "named" (by file system path) sets of dependencies that are automatically "activated" when you start up the Python interpreter. In the setuptools/bundler style you have in memory sets of dependencies that are activated by calling a particular API, often done automatically via a binstub.