I went through the bad/unknown packages in the python3.5 transition tracker
[1] and the remainder seems reasonable for doing the transition.
Many of them only build support for the default python3 and so they will be
bad until after they are rebuilt following the switch. I filed bugs with
patches for packages that seemed to be ~easy to make build for multiple
versions.
Some of the remainder should not be build-depending on python3-dev at all
since they don't have any arch specific content. I filed a stack of bugs on
those too (as well as doing a team upload or two).
That should leave in the neighborhood of 45 - 50 binNMUs, which isn't so many.
Does anyone object if I go ahead and ask the release team for a transition
slot?