Apple has let this model sit for so long, it's hard to imagine what may happen. What is known, is the fact that Apple's riding high on fat profits & astronomical sales of iOS devices. Increases in computer sales are being credited to the "halo effect" of Apple's success.
With much speculation regarding the eventual convergence of iOS & OS X, the future seems bleak when it comes to Apple's continuation of the Mac Pro. Or any professional model for that matter. Now hyper focused on entertaining little devices in their self proclaimed "Post PC Era" they've got that formula down cold.
I'd like nothing better than to see Apple keep OS X & iOS separate, refining each to be the best in the business. Yet it's far too late for that as we're already witnessing.
Apple is firmly entrenched in the Walmart / Best Buy / Super Volume Retail Business. Profits continue to skyrocket with no sign of abating.
I'd say the Mac Pro is either going to get lip service & and a minor bump just to keep Apple from taking any heat, or worse... silently removed from the lineup.
That's *my guess* regarding the model I've used for years quite happily.