This is a topic that has come up before.
I would like to develop a MAC version, but at the moment I'm working very hard on completing the next PC version. Developing a MAC version would take the better part of a year of hard work to bring to fruition.
I'm somewhat torn over which to take on next - I have had calls for a Linux version, a MAC version and also a Pocket PC version. I've done development before for all three platforms, but I'm not sure which would be most widely accepted.
In the meantime, I'm trying to make sure the PC version has all of the features people expect.