provide code freeze facilities for PPA's (some are used to do software distribution)

Can you explain a bit more background behind this? I'd like to understand the bigger picture.

Being able to enable/disable an archive permission instead of being restricted to just adding/removing allows one to maintain the permission list for an archive while still being able to disable those permissions. An example use case would be a project is using a PPA that has a period of code freeze around releases where it would be desirable to prevent uploads from all or just certain users/teams. After the code freeze, we'd currently have to recreate the archive permissions which will require maintaining that data elsewhere for the duration of freeze. It would be less error prone, less overhead, and reduce the need for any resources to store that data while it exists outside of launchpad if that information never had to exist outside of launchpad which would be possible if permissions could be toggled between enabled/disabled.

This is a bit of a hack to get around the fact that PPAs don't have
upload queues or freezes. I'm very reluctant to implement anything like
this, especially since the ACL model applies to more than just PPAs,
i.e. Ubuntu.

A better solution is to actually implement a frozen PPA, or allow PPAs
to have the same states that a distroseries has and restrict upload
access based on that. I'm not sure yet how to fit in a restricted list
of uploaders as opposed to a total upload freeze though, I'd need to
think about that.