In the quest to remove Python 2 from the default desktop install, we're down to just a handful of packages. Most problematic are samba-libs due to upstream's position on Python 3 support and the difficulty in porting that stack to Python 3.
Two packages which transitively keep Python 2 on the install are deja-dup-backend-gvfs and gvfs-backends, due to the dependency through samba-libs. One way to approach deja-dup-backend-gvfs similarly to the way python-gi and duplicity are currently handled, which is that they are installed on demand.
I suggest demoting deja-dup-backend-gvfs to a Suggests of deja-dup (similar to currently deja-dup-backend-cloudfiles and deja-dup-backend-s3), and modifying the install-pygi.patch to install this package on demand. This should prevent gvfs-backends from appearing on the iso by default, but it should get installed at that time too. I have a proposed patch that seems to do the trick for me.
Hoping mterry can review!