[Import-SIG] Rough PEP: A ModuleSpec Type for the Import System

[Nick Coghlan]

This generally looks good to me. Something I'm wondering:

Q1. Can we experiment with this as a custom metapath importer?

A1. Not really, because we want to use it to avoid some of the other
importlib additions made in 3.4. However, a backport to 3.3 as a
custom metapath hook may still be interesting.

Q2. Given this idea as a foundation, could we experiment with ref file
support as a custom importer?

A2. Quite possibly, which may make that a good thing to defer to 3.5
(for stdlib inclusion, anyway).

I'll wait until the updated version gets through before commenting further :)

Cheers,
Nick.