I think it would be useful for Python to accept imports of standalone files representing entire packages, maybe with the extension .pyp. A package file would basically be a ZIP file, so it would follow fairly easily from the current zipimport mechanism... its top-level directory would be the contents of a package named by the outer ZIP file. In other words, suppose we have a ZIP file called "package.pyp", and at its top level, it contains "__init__.py" and "blah.py". Anywhere this can be located, it would be equivalent to a physical directory called "package" containing those two files. So you can simply do "import package" as usual, regardless of whether it's a directory or a .pyp.
A while ago I wrote a program called Squisher that does this (it takes a ZIP file and turns it into an importable .pyc file), but it's a huge hack. The hackishness mainly comes from my desire to not require users of Squished packages to install Squisher itself; so each module basically has to bootstrap itself, adding its own import hook and then adding its own path to sys.path and shuffling around a couple of things in sys.modules. All that could be avoided if this were a core feature; I expect a straightforward import hook would suffice.
As PEP 302 says, "Distributing lots of source or pyc files around is not always appropriate, so there is a frequent desire to package all needed modules in a single file." It's very useful to be able to download a single file, plop it into a directory, and immediately be able to import it like any .py or .pyc file. Eggs are nice, but having to manually add them to sys.path or install them system-wide with setuptools is not always ideal.