Not sure whether you are aware, but the PyRun project I'm maintaining
does that and goes beyond this by freezing almost the complete stdlib
and statically linking most C extensions into a single binary:

https://www.egenix.com/products/python/PyRun/

Startup is indeed better, but not as much as you might think.
You do save stat calls and can share resources across processes.

The big time consumer is turning marshal'ed code objects back
into Python objects, though. If that could be made faster by
e.g. using a more efficient storage format such as one which is
platform dependent, it'd be a much bigger win than the freezing
approach.