Is end-to-end encryption going to be part of a modern IRC experience? Please, this is an absolute must. And don't make it optional if possible. Make non-e2ee optional.
There's been a number of E2E encryption methods proposed in the past such as SSL/TLS DCC (which doesn't do certificate verification from what I've seen, so that's not too useful here), FiSH and OTR are already used decently out there but I'm not aware of any widely-available, simple-to-implement specification for clients to look at. There's another interesting proposal here, but it hasn't gained traction as of yet: http://blog.bjrn.se/2009/01/proposal-for-better-irc-encrypti...