Could be you! Context switching accounts doesn't seem like too difficult a task.
Except I’m not using protonmail since I trust my yubikey way more in terms of storing my private keys.
Also, it only seems like a simple task. You still have to manage notifications and UI for multiple accounts. Not to mention that I’d probably not do that free of charge.
And I was wondering if someone could add support for signing/encrypting emails on the ProtonMail iOS client with openPGP keys on my Yubikey? :)
I'd rather finance an iOS Thunderbird with GPG support.