I received a reply from EFI, the makers of the Fiery products this morning.
Apparently the EFI tools themselves run fine under classic, and Carbonated versions are in development.
I am of the understanding that the OS9 Fiery PPD may be able to be used in print centre in OSX, though I have yet to try it. I know of at least on Design firm in the UK that is using the standard Canon PPD from OS9 in this manner.
As for "no print studios switching to OSX", I guess that must be just in your part of the world, because down here in New Zealand, I know of at LEAST 2-3 studios that we deal with which are integrating OSX machines into their workflow's; and while there have been some teething issues as one would expect, the feedback has been overwhelmingly positive as a result.
I look forward of dragging my studio off it's addiction to the user friendly, but weak & comparatively unstable traditional OS9.x system onto an OS that can really let me do some work.