the closest thing to WINE for mac is GNUStep, which afaik does not run pure OSX apps of recent vintage, certainly not without a recompile and removing all sorts of stuff Apple has added in the past decade...so it would be unsuitable for AU plugins. what do you mean Mac emulation? if you are talking about PearPC, or MacOnLinux, you could run an entire VST/AU host inside of that and shuttle the audio across via wormhole/audioverlan/Jack-AU etc.. similar to what you could do running a windows VST host in VMWare as for running the plugins directly, NetBSD has already got OSX Binary emulation going (on powerpc) - i would expect this situation to improve rapidly and extend to linux as more people begin to use the Intel version of OSX...