Is your feature request related to a problem? Please describe. Currently for e2e encryption the most popular solution is OMEMO, however due to offering forward secrecy it's impossible to maintain access to archived messages from other devices. Using OpenPGP could be an interesting, alternative solution here:

XEP-0373: OpenPGP for XMPP XEP-0374: OpenPGP for XMPP Instant Messaging