Comment 4 for bug 157034

I don't think this in fact has anything to do with the ubiquity-preserve-home specification. This is a request for default mountpoint assignments to be detected automatically.

I am inclined to say, though, that if you need this badly, you are not making very effective use of Ubuntu's built-in upgrade tools! Most people don't need to reinstall so frequently that having to assign mountpoints is a major hassle.