There have also on and off been discussions about building arbitrary patches as they are sent to the mailinglists. Doing that without any committer (or other trusted party) as a filter is a completely different challenge of course, given that it basically amounts to downloading and running random code off the internet.
Perhaps https://travis-ci.org/ or something similar could be used for this. That avoids any issues about random code.
AFAIK travis-ci would require us to use github as our hoster for all those things, and embrace that workflow, they don't support anything else.
