All very true, but if we can't improve both sides then we are simply going to end up with even more patches that we take a while to get around to. I want to end up with a solution that advances the situation for *both* committers and non-committers and I feel like that is being lost in the discussion somewhat. As the person who pushed for a migration to DVCS for non-committers I totally support improving the workflow for non-committers, but not at the cost of ignoring the latter half of the contribution workflow of committers which is a chronic problem.
As the PEP points out, the devguide, devinabox, and the PEPs have such a shallow development process that hosting them on Bitbucket wouldn't be a big thing. But if we don't view this as a long-term step towards moving cpython development somehow we are bifurcating our code contributors between git and hg which will be annoying. Now it could be argued that it doesn't matter for the peps and devguide since they are purely text and can be done easily through a web UI and a simple CI in Travis can be set up to make sure that the docs compile cleanly. But moving devinabox where there is going to be a code checkout in order to execute code for testing, etc. will be an issue.
So I guess my view is +0 for doc-only repos on GitHub as long as we make it clear we are doing it with the expectation that people will do everything through the web UI and never have to know git. But I can't advocate moving code over without moving ALL repos over to git -- hosting location doesn't matter to me -- to prevent having to know both DVCSs in order to do coding work related to Python; the cpython repo shouldn't become this vaunted repo that is special and so it's in hg long-term but everything else is on git.