I just realized today that since the only drawback of the wonderful wonderful WKD is that it needs serverside support… chatmail could add it! Since it’s already it’s own server. And then become compatible with Proton and others. The install base of encrypted mail would join like two amöbae on acid! WKD lookup is something I’ve dreamed of before already so here’s one more reason to.
But speaking of chatmail. I had a bad experience with a chatmail user today (I was on vanilla postfix/dovecot, not chatmail) because it has the “first message problem”. With normal autocrypt you can send one message and from then on you’re off to the races and it’ll be encrypted from then on. (WKD doesn’t need this, it can be encrypted right away.) But since chatmail can’t send unencrypted you can’t really bootstrap the convo! Except for some weird Delta Chat-specific link! We also tested that I sent an unencrypted-but-with-autocrypt-headers email to him and that did not get through either, it bounced with a 523 Encryption Needed: Invalid Unencrypted Mail. Conclusion: chatmail has a vendor lock-in problem! 
I would’ve wanted Delta Chat to move in the direction of increased compatibility with the wider email/PGP world, not away from it 