I would like to suggest that Deltachat apps should learn how to configure an account from a QR-code.
Email-providers could then generate QR-codes for their users (or admins could generate them for their organisational members, or group-techies for their allies), in order to make it even easier to get started with Deltachat.
As far as I know there is no (living) standard for encoding credentials in a string. I’m only aware of QR-codes that contain a URL to download a configuration profile (e.g. fastmail.com). But those are OS-specific, more complex and maybe not even well applicable?
So I think you would be free to invent your own scheme. But it might be easiest to just re-use the response format of mailadm?
(It might be useful to think about the extensibility of the scheme: I can e.g. imagine that organisations would like to include an email-address into the QR-code, which is used to open a chat with and compose a draft á la “I made it”, that only needs a tap to be sent. This way the sending admin could know who successfully set up their Deltachat app, and could then invite those people to a group.)