A souped-up iMac and some sort of thunderbolt 'bay' for expansion cards would serve the pro market, one would think. A large-scale touch display would be on the wish-list as well. That's my complete guess as to where they might be headed. I can't really imagine that Apple is unaware of how important the pro market is to their image, if not the bottom line. Consider the strong ties with Pixar – they must get constant feedback into what a pro setup needs. I'm betting on a big iMac/Pro update in the fall.
There's nothing wrong with the Mac Pro but the whiny ones who can't afford it or prefer to scoff at the price rather than recognize the value. Yes, we all want a smaller "Pro" system you can upgrade, but there's no market for it.
The sad truth is Apple sells only "thousands" of Mac Pro systems compared to "millions" of their more mainstream products. That they make them at all is interesting considering the expense that must go into designing them.
It's possible as Apple makes an increasing proportion of their revenue from iOS and are less threatened by the possibility of losing control of a portion of their OS X market that they might allow a few select manufacturers to produce and support a true workstation-class system. For Apple it'd be checks in the mail for licensing fees and an almost imperceptible loss of market share.
I'm aware of gorilla arm, and sure, that's an issue with an upright display... but I see no reason why you couldn't have the display on a swivel – like a drafting table. Swivel down, and the display becomes a table-top. Swivel up for traditional computer interaction.
As far as Apple licensing OS X, that seems highly unlikely given how things went during the 1990s with Apple clones.
What's important to remember is in the 1990s the Mac business was the vast majority of the then "Apple Computer" company's revenue. Today it's a small and shrinking percentage.
