In preparation for the hg switch, I would recommend that, if you have any feature branches managed with svnmerge, you sync them with the py3k branch before we switch. That way, it will make it easier to "bridge the gap" when you create a new repository for your work after the switch (the svnmerge information isn't retained in the converted repo).
Is that really going to work? I.e. will Mercurial be able to merge from default to one of the feature branches? If so, what will be the procedure? What would be the exact steps to try this out on the PEP 382 branch (say)?