The point of this suggestion:
With the introduction of tags to the Assistant, the experience of organizing threads was significantly improved. Quite a few of us use the Assistant with the thread saving setting set to 24 hours.

When adding a tag, the user likely intends to have the thread remain for the foreseeable future since they are going through the effort of adding tags. Therefore, it would make sense to have the first added tag automatically remove the Temporary tag. The user could still manually add it back, if they so desire.