Thanks for your comments mths.
I think it would probably make sense for mIRC to hide ISO channels in /list. It may even make sense to /part an auto-joined ISO channel and automatically /join the UTF-8 version. That would migrate many users to UTF-8 automatically.
I dont know if that sounds like a good idea, this means alot of people need to rewrite/update there servers, and they need to do it for 1 program people use to chat with, it's many others out there, and i for one belive this will force many users to stick with a outdated program. (mirc v6.x)
And as argv0 said, "QuakeNet, and I'm seeing maybe 5% of the registered channels with UTF-8 incompatible channel names.", i using åäö in my language, and many channels im in using some of the letters, and QuakeNet is only one network. Think of all the other networks to, there you find many more channels and users joining channels with UTF-8 incompatible channel names.