Honestly, which those Bench Test's and speeds and all the goodness that the New Mac Pro is showing, 7 Teraflops of Computing Power, 2.5 times the speed of the new Flash, 20GB/s data transfers to a Backup Array, Power to connect 3x4K Displays, Bluetooth 4 and ac wireless, Why Dennis would you want to Upgrade anything in it, honestly. But I'm sure you will be able to swap out to bigger Flash ??
It's impressive, no doubt. And maybe my vision is clouded by the mindset of a tinkerer/old school geek (and no doubt, Dennis agrees with me here as well). But if I were doing REAL work with a $3000K+ system (and I believe this Mac Pro will be significantly more costly, given the state-of-the-art Flash-based storage), I would not want a "locked" box full of proprietary hardware that I can't take a screwdriver to.
Additionally, given that Apple won't provide warranty support beyond 3 years for its hardware, I would live in constant fear of eventually having a 3-year-old fancy looking doorstop should it experience even the slightest failure.
Now, that's a LOT of speculation, because we don't know all that much about it. But given the recent trend in Apple hardware, particularly with the latest iMacs and Retina MacBooks, I'm guessing that speculation isn't far from the truth.
The thing that bugs me the most is that there is no reason from a technical standpoint to build a machine this way. This is strictly a design exercise, much as it was with the recent iMacs and Retina MacBook Pros. Believe me, I get that this is part of Apple's DNA and that function will always follow form. But I believe that in the past, Apple has done a much better job of innovating in design without throwing all practicality out the window.
To take it one step further - automobile manufacturers release concept cars every year. They are usually "pie in the sky" designs that feature a theme or design language that will eventually trickle down into mainstream models, but in reality, they're not completely functional. Sometimes you can't open the hood, or the vehicle can't move under its own power.... This is like Apple creating a concept heavy duty pickup truck and turning it over to production with a full tank of gas, but no fuel filler door.