Now, to do ALL that (but starting from scratch) for another OS would be impossibly time consuming
Why can't the windows version just be ported over? It's C/C++ afterall and that's what one of Linux's greatest strengths is: development of C/C++ code. Plus, as far as I know, it's not dependant on any Windows files. I'm sure porting would only be a minor job.
I personally would LOVE to see mIRC ported to Linux. Linux, in my opinion, lacks a really good graphical IRC client (XChat is okay but doesn't come close to mIRC) and running mIRC in wine is... well... 'special'.
Regarding what one of the previous posts said about GPL: Khaled isn't obliged to give away mIRC and its source just because it happens to run on Linux. He doesn't HAVE to GPL it if he doesn't want to. It can still remain under its original shareware, closed-source license.
I know it's not likely to happen any time soon (if at all) but I'm sure I'm not the only one who misses mIRC