Would this be a good time to put kfreebsd-9 in experimental?
Yes please.
Is there any point in keeping kfreebsd-6 and kfreebsd-7 directories in SVN? I think they could be removed.
They are still in oldstable, it does not cost much to have them in SVN.
As for kfreebsd-7, its package is still in the archive. This wasn't included with squeeze, should removal be requested?
Yes, with note that it will be replaced by kfreebsd-9. Petr