Add support for the machine-readable format, like JSON e.g. (or another common one).
And, probably address all Mailpile.is complaints:

https://www.mailpile.is/blog/2014-10-07_Some_Thoughts_on_GnuPG.html

https://www.mailpile.is/blog/2014-11-21_To_PGP_MIME_Or_Not.html