Getting them to manage additional keys, and get them signed and registered appropriately, and then supplying them is going to be a similar amount of work, and the purpose is far more cryptic and confusing. My proposal is basically that instead of asking developers to manage signing keys, we should instead be ask them to manage account on a validation server (or servers).
I need to think more about the rest of what you’ve said (and I don’t think it’s a short term problem), but I just wanted to point out that “managing keys” can be as simple as “create a secondary pass(word|phrase) and remember it/write it down/whatever”. It doesn’t need to be “secure this file and copy it around to all of your computers”. Likewise there’s no reason that “delegate authority to someone else” can’t be something like ``twine add-maintainer pip pfmoore``.
PGP: 7C6B 7C5D 5E2B 6356 A926 F04F 6E3C BCE9 3372 DCFA