Obviously, channels are the best way to accomplish a "multi-client query." On another note, however, multi-client DCCs (loops) may be significantly more useful, especially in the event SSL DCC
is implemented and clients desire their traffic to be private, but do not have the capacity needs to make setting up a secure IRCd worthwhile. I assume the only way to effectively accomplish this would be to have direct connections with each participant--else mIRC is acting as an IRCd, anyway.
Though this doesn't seem to have a ton of application right now, I'm a general advocate for seeing mIRC become a client capable of direct and secure communications. As far as I know, there aren't really a lot of other low-resource yet direct/secure ways for even two people to easily communicate, let alone three.