In the conservative version of this vision, Perl and Python have different runtimes dynamically linked to an instance of the same opcode interpreter. Memory allocation/GC and scheduling/threading are handled inside the opcode interpreter but the OS and environment binding is (mostly) in the libraries.
Hm, the Python bytecode interpreter doesn't do the memory allocation/GC, and only does the scheduling/threading indirectly (by releasing and immediately reacquiring the global interpreter lock).
Things Python would bring to this party: our serious-cool GC, our C extension/embedding system (*much* nicer than XS). Things Perl would bring: blazingly fast regexps, taint, flexitypes, references.
I'm not sure I want references, and I don't know what flexitypes are. --Guido van Rossum (home page: http://www.python.org/~guido/)