1. I think many of these uses have been made obsolete by the automatic pingbacks that appear when an Issue/PR is mentioned elsewhere. For example, in PR
https://github.com/sagemath/sage/pull/36951, I included the text "- Part of
https://github.com/sagemath/sage/issues/33577", which created a "This was referenced" message over there.
2. Additional links can be added just by posting a reply in the Meta-Issue. When it becomes useful to incorporate it in the description, either the original creator of the Meta-Issue and also anyone in the Maintainer role can do so.
3. The current assignments of roles in the GitHub project (above the level of the Triage team; in particular Maintainer and Admin roles) are the result of a not very clearly defined process. Now, 1 year after the migration of Sage development to GitHub, it would probably be a good timing to establish a clear process and review the current role assignments.