I think a Phabricator tag related to tasks about porting Python 2 to Python 3 code would be valuable for those interested in conducting/helping/reviewing porting efforts.
Maybe #python3porting
Example tasks that would get this tag: T218427: Upgrade various Toolforge infrastructure scripts from Python 2 to Python 3, T218426: Upgrade various Cloud VPS Python 2 scripts to Python 3, all subtasks of T242120: Python 2 to 3 support request.