Do "we" really need it? SSL is a fine enough encryption to secure your data between your node and the server. Privacy is cool and everything, but FISH is overboard and unnecessary for most users.
There are also ways to implement encryption without patching mIRC, and I see no problem with third party scripts here. The whole point of mIRC's robust scripting support is for cases like these, where a smaller demographic might need a tool that does not really belong as a core feature of mIRC.