Audio/video chat hasn't been around (widely at least) for more than 10 years, and it's been available in conjunction with IRC (or rather it's supported sub-protocols) far less time than it has existed on the net in general. IRCle may have been first developed in the late 80's but it didn't develop support for DCC AUDIO and DCC VIDEO until much later.
There's no way for either me or you to know if support for either of these things has been seriously considered in mIRC or whether it is intended to be added. Yes, it is possible obviously. The question is whether it's practical and worthwhile to implement and, if so, precisely how to do it. There are numerous IRC clients that support audio and video communication initiated via IRC, however they use several differing methods, each with their own issues in regards to portability or availability across systems. So you see it's not simply a case of deciding to add support for audio or video via IRC. It's a question of which way to do it, or whether a new way should/must be made to do it. And if it does come to that, designing a streaming protocol or sub-protocol is certainly not something to head into lightly.
While I'm not against video or audio chatting being supported by mIRC, I think it's important to point out that text chatting isn't at all inferior or less useful than them. In fact many things are far easier to communicate as text.
