Supposedly Mac OS X already has the largest installed base of any single *nix distribution and certainly is ahead of Linux on the desktop. So there are easily as many potential users of Wine for Mac OS X as Wine for X86-whatever. And Virtual PC has been popular & successful.
Actually, according to figures from Apple and IDC (guess which is more neutral) desktop Linux has at least double and possibly quadruple the installed userbase of MacOS X. I have pointed this out several times when people make statements such as that, and have yet to be refuted, so be careful when saying things like MacOS is "certainly ahead of Linux", as the statistics don't back that up. *shrug*
Bear in mind that to actually do a MacOS port would require rewriting quite large parts of Wine even if you still use an X server, and then Windows apps would still look like Windows apps, not Aqua apps. Please don't get discouraged, but you should be aware of how much work it involves before starting. As CPU emulation would be one of the trickier parts, I'd definately go with the advice to start by making x86 binaries work on Linux/PPC, as that keeps the number of things that could interfere to a minimum.
ta -mike