I see both sides of the argument, I guess. Also, since I'm in the market for a new Mac and have always owned at least one of Apple's "Pro" line machines, I'm giving this plenty of consideration.
It's hard to dispute that this Mac Pro has much less (almost nothing, really) in the way of internal expansion options. That's always been half the point of the Pro line. There are all different kinds of "pro" users -- video editors, photographers, audio types, coders -- and they all have unique needs for the kinds of interfaces and accessories they need to add to their workstations.
Some of us -- people like me -- will do just fine with a Thunderbolt breakout box. I want a big monitor (or maybe two, or three), lots of storage (at least some of it fast), plenty of USB ports, and a way to connect a firewire audio interface. A Mac Pro with one of the several Thunderbolt breakout boxes would encompass all my needs. I can't really complain much about the $250 or $300 for the Thunderbolt device if I'm considering spending $4k on the computer itself.
I suspect many "Pro" users are in the same boat as me. They may complain about the lack of user-expandability, but they'll find a way to do everything they need to do. Many will complain that things aran't the way they used to be, but this has ALWAYS been the case with each new major generation of Apple hardware. People complained when Apple dropped floppy drives. They complained when Apple dropped the serial connector. They complained when Apple dropped the optical drive from the iMac and all the portables but the Macbook Pro. Apple does this by design, generally. They force people to get rid of their shitty old floppy drives. Quit looking backward, start looking forward. People will complain, at first, then a few years later they'll understand why Apple forced the issue. Does anybody NOW question why Apple killed the floppy drive, the serial port? Soon, it will be the same with even the ubiquitous optical drive.
I've been following Apple for a long time and have seen this cycle of crying and moaning over and over. Some generations of Pro machines have been better received, others worse received. There has ALWAYS been complaining, and a large number of people always throw their hands up in despair and say "Apple has forsaken me -- I guess I'm switching to Dell (or IBM or Silicon Graphics or Sun Sparc or fill in the blank)." I'm not saying their complaints never have any merit -- just that there is always complaining, always a lot of talk about how Apple has clearly blown it and will now irrevocably lose the Pro user.
Also, I think many of the people laughing about the Mac Pro (It's small! It looks like a trash can! Is Darth Vader living inside?) are just being silly. This is a power machine for serious work.
Having said all the above, I do think Apple has let down a small segment of its professional users. As the guy in the video above says, for SOME people, having 4 internal, always-connected, always-powered, maxed-out SSD drives is a huge benefit. Telling those people to just add stack after stack of external drives is an answer, but not really a good answer.
Also, many such users have unusual needs for graphics processing or i/o options not easily convertible to Thunderbolt. What if you have thousands of dollars worth of PCI Express cards? Yes, you could buy a Thunderbolt PCI expansion chassis, but it seems like we're saying over and over "just do it through Thunderbolt." It's not as if these machines have 24 Thunderbolt 2 ports. At some point, all your Thunderbolt ports are used-up, your bandwidth maxed, and you want to add one more thing.
Bottom line, those of us who aren't REALLY "Pro" users, or who are only on the border of "Pro" level requirements as far as processing power and expandability, will do just fine. In fact, I'm not sure I need to buy something as powerful as one of these. They're expensive, and I might do just as well with a maxed-out iMac 27. Computers these days are FAST, when your needs are just digital audio recording/editing, and a bit of graphic design. I could probably get by with a maxed Macbook Pro Retina, too.
But it does seem a shame that Apple has arguably abandoned several niche segments of "Pro" users. It would be different if they marketed a separate Thunderbolt 2 chassis with slots for 8 internal SSDs, a couple of PCI cards, and a whole ton of Thunderbolt and Thunderbolt 2 pass-through ports.
I really do see both sides. I think there's a lot of unnecessary complaining, and many people's needs will be met perfectly well by these machines. At the same time, I think some users really are not well-served by this new Pro. Those users should probably buy a current generation 12-core Pro, put in 64GB RAM and hook up a Thunderbolt 2 SSD RAID, and they'll be OK at least until Apple comes out with a revision or two. Who knows what the third or fourth revision of this generation will be like?