It isn't likely, since most of the high-end shops have a lot of custom software on those Linux machines, and even their Linux distros are in many cases heavily customized, beyond what they'd be able to do with OSX.

Smaller FX shops that don't have IT staff are much more likely to consider it, unless they rely on software that isn't available in OSX, like XSI.

Which reminds me, now Houdini is available for OSX (it might still be beta, but it's coming if not here already).