I have a non-core dev willing to help maintain the cgi/cgitb modules along with myself.
Would this consist of adding the both of us as experts on those modules, and then I would be responsible for the mechanics of approving/merging any PRs?
I don't think there's anything technically preventing folks who are not core devs from being added there, but I would expect them to at least be triagers as they will get nosied on appropriate issues.
Assuming this individual does well we should make them a core-dev at some point, but presently they have no experience contributing to the Python codebase.
I assume it would be the same as what Barry is doing with two other folks on the 'email' package: treat it like a mentoring situation and if they work out you an put them forward to become a core dev.