Hi David,
Linux a no go for Adobe. I really wouldn't worry too much about the MacPro. I doubt it will be killed anytime soon.
While you could argue that they killed FCP, well they didn't really, the MacPro is pretty much Apple's only high end machine and I can't imagine them killing it now. And by the time they do, you might be editing on an iPad :-)
We use both MacPro and PCs and while I have come to prefer OSX for its simplicity, I would have no problem trusting either one for a long haul project.
Vince Becquiot
Indigo Live
San Francisco - Bay Area