I think I can upload both packages with both Python 2 and 3 (easy) and then we can wait for Mercurial to switch over and drop Python 2. I’ve done that with hgsubversion already.
I can do this as well with mercurial-keyring, if that is an option. I was under the impression that you need a "python[3]-" prefix to do that, but apparently not.
Christoph, by the way, how about moving these two packages into DPMT? They already have a Git repo for an ancient version of mercurial-keyring (which I replaced with yours), I could move extension-utils there as well (I have a Git history locally).
I guess this would be a good thing. I started playing around with git-buildpackage anyways, but on github:
https://github.com/eraserix/mercurial-keyring I'll create an updated version of mercurial-keyring with both python2 and 3.
