You could have the additional key be offered by the person who onboarded you too 🤔

Like an “affiliate + key assistance” system. As long as they understand the trust model, this could be an interesting idea.

Also I think a way to hold the “backup” key with a friend or spouse using Apple keychain or Google password whatever would be critical. I think having them use an entirely different app and download it would be a bit friction for someone who didn’t have any bitcoiner friends. But if you could have a way to have a secure keychain encrypted key or something, and your wife or friend could just scan a QR and unlock something for you, that would be good UX. They wouldn’t even have to know what keys are being used or where. They just know that their Apple account has the keys to help get your coins back. 🤔🤔

Something there I think. 

 I love this idea. Ties in well with WOT concepts.

Additionally, id like to see this software signer take the form of an open source app that would work across any exchange or service that supports it.

Think something like Amber or nos2x, but for Bitcoin keys (obviously never for single-sig).

The app would also house configuration files for the multisig wallets it contains keys to, and would reject any attempt add additional keys from the same multisig as a security measure.