But the updated packages may not like old configs. There is still potential for occasional problems there.
>It's a clean installation, I don't think it needs any magic. Also
>third-party repos are not a problem, we just ignore them and they
>won't influence the new system. People will add them manually again
>once in 18 months.
There is desktop config in people's home directories that may not
work with
updated packages as expected.
Package updates don't touch your /home. Clean install is the same as package updates in these regards.