Avoiding links is the ultimate goal, hopefully Tutanota will integrate your suggestion or something similar. I've moved my entire family to Tutanota, which also works quite well. But you'll never convince everybody...
As far as I know self-destruct emails in Gmail are not end-to-end encrypted.
Why can't these services use something like OpenPGP's Web Key Discovery [0] fetching key from https://domain.com/.well-known/openpgp/hu/hash-for-localpart and avoid links altogether?
[0]: https://www.gnupg.org/blog/20160830-web-key-service.html