If IRC suffices for your purposes, then Matrix, with its encryption and all, is apparently overkill.

If I were to upgrade an IRC-based community to something newer and richer, I'd go with Jabber, well-known, well-established, with a ton of various clients and several servers. Yes, it's not ideal, but it's still a massive upgrade compared to IRC, if your server supports a good list XEPs and your community members agree to use non-esoteric clients that also support them.