@nicfab @yawnbox I have lived through essentially the same issues with PGP keys in DNS, hashes of SMime keys in DNS, MTA-STS, DANE for SMTP, automatic SMIME using SMILE, etc.
I hope WKD does better! But I fear that without a solution to local email search it will be a victim of its own success, or you will have to put so much information in the subject line to remind you what is in the encrypted body that some privacy is lost.