Given that email already has long established standards, mostly being followed, there are only a couple of changes, neither very radical that need to be made. One is to ban the use of any that don't follow the standard - I wonder who that would be - and the other is to roll PGP into the standard. In regard to the last PGP itself has been available in email clients for years, nothing new there.
Public key distribution would appear to be the main issue. It's not as if serving small text files is a massive technological leap. The only problem is telling the punter where to find the server. There are a few possible alternatives. One is to add a new type of record alongside the MX record to point to the key server. Another is to extend SMTP to allow the mail server to query the location of the key server. A third would be to have the mail server function as the key server and extend SMTP to request the key.