This will be quite easy to do...in the context of native apps. Generating the code and showing it is trivial, the tricky part is reading it. I'm pretty sure it's possible but don't think it's very easy to do at the moment using mobile web browsers.

Given the marginally better experience this would create, I don't think it's worth much developer time at this stage. If and when native aps are developed for accessing the site API this will be a great little feature.

For MFA[^note1], providing QR codes makes a lot more sense since TOTP[^note2] storage apps typically already have built-in functions for reading them.

[^note1]: Multi Factor Authentication
[^note2]: Timed One Time Password