I believe it may be a bit of a headache for Khaled to implement, although some better interface to intercept outgoing / incoming messages?
Perhaps you could simply write a form of bnc / socks proxy or such that can intercept PRIVMSG and encode/decode transparently on the fly without affecting mIRC, other than say perhaps mIRC dialogs / menu's to tell the program proxying how to do its job, encrypting to a person / channel, getting keys and so forth.
Point being perhaps there it a better way to add such functionality using widely avaliable code via a more transparent means as its really a matter of applying encryption in the appropriate layer, and less hassle for people who dont want to use it and be taxed by a 100-500k increase in mirc exe size, by something that could quite easily be implemented in a less intrusive manner.