I don't know about "try" -- personally I don't see a difference for the release procedure, no matter where the source comes from.
I guess you haven't done a release yet, then :-) Assuming you are going to use https://svn.python.org/projects/sandbox/trunk/release/release.py then you'll have to port that to Mercurial, first. Or, you write your own release tool, as any serious release manager did so far :-) As for the Windows build, I don't know how to do "externals", yet. In particular, I don't think it is a good idea to have all externals in a single Mercurial clone: due to versioning, we have multiple copies of them, which will take quite some space. As a minor problem: I currently have a batch file head.bat, which updates sysmodule.c after a switch to expand HeadURL correctly. Not sure whether this will be needed on Mercurial, or whether the build identification patch is able to learn about tags in the first place. Finally, I wonder how the documentation build process will continue to integrate subversion. I guess you just need to have an svn binary around when building the documentation. Regards, Martin