I think you're making it into a bigger issue than it is. I've just been doing surveys of networks like Undernet and QuakeNet, and I'm seeing maybe 5% of the registered channels with UTF-8 incompatible channel names. It might be a really big deal to those 5%, and I completely understand why and sympathize, but those users can always stick to 6.35 if they need this support. The other 90+% of users will greatly benefit from UTF-8.
The security side of this is relatively bogus. Besides EFNet, there are really no networks without services support. More importantly, opers aren't drones. If a user registers a the unicode equivalent channel name of an existing codepage channel in order to gain control of a channel, an oper can quickly out whether the use is legitimate or not and decide whether to revoke the registration.