I'm also leaning towards a dead Mac Pro. I think it's quite clear that if you're a professional who needs something like a Mac Pro, you better start planning to convert to Windows 10 now.If it doesn't happen then, the MacPro is dead.
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The current gen MacPro was released at WWDC 2013 (wow - 4 years ago). If it doesn't happen then, it's not going to happen.
Even if it does get refreshed now or at some point in future, you still couldn't rely on Apple for regular updates. In fact, I suspect that the current Mac Pro design will be the last Mac Pro, going the way the iPod Classic.