Making a 7.8 the traditional way still requires an "mv 7.7 7.8" in the cvs repo, with whatever effects that has in the exports. At least this time we'd know the exact moment when it occurs.
As for the svn export, the name of the directory doesn't really matter (I just need to add a single line to the top level to use a different source path for that particular repos), so I'm fine with such a directory rename if we go for a "partial switch" plan.