Not saying this is a bad idea, but it will put a load on the admin team because adding a tag to the required tag set requires admin permissions.

Secondly, it poses a UI problem (image). The list of required tags will likely only grow.

I wonder if there's a way to reduce the admin burden without introducing too much chaos.

What if anyone could add a proposed community tag, but only admins could delete/downgrade them?

For the UI problem, dealing with that might also help if there are other instances in future that have other reasons for larger numbers of mandatory tags.

Even so, we would probably need to make sure mandatory tags are deleted as their proposed communities migrate, so the list doesn't get too long.

Data integrity may be an issue if a required tag is deleted, since posts that use that tag won't have it anymore, causing them to have zero required tags.

IIRC, this has been tested before and found to not visibly break things since I believe the requirement is only checked at submission, but it's still worth thinking about since it is not a state that the system currently expects.

Yes it's probably worth implementing a check at migration stage. Ideally the migration of all of the questions for a given community tag should leave none remaining with only that community's tag.

A question with more than one community tag would presumably be copied to the new site rather than migrated, so that the original remains for the other communities. In this case the migrating community's tag can safely be removed due to the presence of other community tags.

There are probably other edge cases we won't think of so having extra checks in place seems sensible.

It wouldn't be more of an admin burden than adding it to the "topic tags" list, which is what we do now.

For proposals that are no longer active, we don't have to delete the tag, just remove it from the list of required tags. If a question has more than one community tag and we're going to launch one of them, we'll ask the people involved to decide what to do with that question first.