Not trying to be cynical, but besides form factor, what's revolutionary about this Mac "Pro"? They've done it before with iCube, the iMac on the stick (with a dome base, in face of predominantly square computers back then and even today). But otherwise, what's revolutionary here, I just don't see it?
With quicksilver PowerMac G4 - it was revolutionary, because unlike PC (and I've always build my own PCs), it could be opened in one motion with all expansion slots very easily accessible. To a bit lesser degree same was with Mac Pro G5. But G5 had innovation that on top of easily expandability, it had smart cooling and almost no visible internal wires.
What's innovative about new Mac Pro? They designed cylindrical from factor with a turbine inspired cooling, venting through the top... OK. Custom design proprietary motherboard to fit into small space (ala dome base iMac) - OK. But that's nice for a light consumer computer, where looks are super important. Heck for Apple pro-user, looks are really important. But what does it bring to the usability that pro users need? How does it improve my workflow when I cannot add graphics card, expansion cards, more hard drives - while retaining the elegant minimalistic looks?
It seems to me Apple thinks Mac pro users really don't need pro features, they THINK they need. Time will tell. But given that, there is no technological barriers this thing broke. Anyone with enough budget can design custom electronics to fit into a specific shape, especially if there is no requirement for extensive expandability.
Marketing talk, that what it is.