I'm betting that he doesn't want to.
Anyhow, mIRC isn't perfect or else the new versions wouldn't include bug fixes. That isn't to say it's not great, because it is. But "perfect" is not really accurate. Besides, he adds new features that people request (if he thinks the features are good ideas) and that alone makes keeping it updated a good thing.
In my opinion it is way more than perfect, as a chat client.
I don't know if native support for tunneled SSH connections or any other mean of encryption (like built-in AES text encryption) has been introduced in newer versions, but this would be the only important improvement needed maybe, for a chat client (mIRC should be just that, shouldn't it?)
Anyway, I still think that Khaled could spend his genious on something more rewarding and important, and leave the mIRC project to the opensource community for further development. But it is my opinion, not Khaled's one it seems, so don't you worry.