As a mac user, i too, want a mac os port, but I doubt it will ever be made. I see several reasons for that:
Firstly, as it was never planned to do cross-platform, making a port to _any_ other operating system would be very expensive in terms of cost and time. You could compare the process to making a client from scratch.
Secondly, by 2008 mabinogi is getting old (about 5 years), so that there is a sequel titled Mabinogi Heroes in Korea. Better or worse it is the next iteration and that makes rewriting mabinogi useless effort.
one could try using software like Crossover. I, myself, have a G5 iMac and the software for the intel's only, so i can't tell if it would work or not.
Should devCat used a more open standards and frameworks like OpenGL, making a port wouldn't be so much work as it is.....