File leachers? You are worried about those?
What ebout people who use IRC to hold meetings and transfer project files (yes, I do know people who do that).... there are legitimate uses. Besides 'leachers' as you call them don't use IRC they use other means, such as Kazaa.

Also you are worried about the developers spending time on XMIT rather than other features?
If the developers are using an object oriented programming language, XMIT will take less than an hour to program. I know, I am a programmer myself. Last I checked an hour is not a lot of time.

Script it?
Ok, so either one programmer codes it in or every one who wants support needs to script it. Also, what about people who odn't know how to script?

And yes, RFC date does matter. Because numerous other RFCs have been released announcing additions to the IRC and CTCP formats. So mIRC is going to ignore the new RFCs and consentrate on the old one?
Nothing has changed in the new ones, just the new ones append to the origional. What you are proposing (although on a smaller scale) is the equivilent of obeying the constitution but ignoring the ammendments.

Why to do it?
* Will only take an hour to program
* Will allow support for newer clients
* Will comply with the newest RFCs
* Will save scriptors time and give the feature to people who don't know how to script.

Why not to?
* Will take time away from other project - not true unless you consider an hour a lot of time
* Will allow leachers/pirates to do faster transfer - true but it will also allow legitimate users to do it to
* IRC is a chat client - true, it is a chat client. But now with instant messangers file transfer is a big part of being a chat client. Why keep IRC stuck in the past?