First, I can't tell much from the picture, so I withhold judgment on the case and its looks. While I love the shiny aluminum of my Mac Pro, it's also as heavy as a Mack truck and has a lot of wasted space, so there may be improvement there. While black is not my favorite color, under my desk, it doesn't matter and on top, well, move over shiny slab from 2001 A Space Odyssey.
Second, yes, I love that I can put four drives in my current Mac Pro, plus have an expansion bay that now ouses my SSD and also have space for expansion PCIe cards, but the premise of Thunderbolt was to maintain the speed and eliminate the need for such internal storage. I currently have two four bay external eSATA drive boxes because of how long the drives last and how long it took to get affordable larger sizes. It would be nice if the Thunderbolt solutions were less expensive, but it takes time to get critical mass and for smaller manufacturers who might put presssure on prices to get the necessary licensing and chipsets to force prices down. We're starting to see some relief, I would hope that this accelerates it. I think that many Mac Pro users are already using external solutions, so removing them from the box and connecting from Thunderbolt, while a pain in the ass to have to figure out inexpensive connectivity solutions, should not pose that big a problem.
Finally, we all know that this comes down to power and price. I will venture a guess that Apple made a choice, either put in the fastest technology and graphics processing ability, while shunting off to externals the storage capacity to maintain its price levels, or maintain the behemoth that the Mac Pro, but raise price points to upgrade the technology. There is no need anymore for there to be four internal hard drives, there are a variety of solutions, so maintaining that internal capacity was an unnecessary cost. While the pictured case is nothing to write home about, I will need to see what it is made of, and decide then. Yes, I like the strength of the current Mac Pro case, but I can't tell anything from a picture, so won't jump to the conclusion that it is cheap plastic.
Bottom line, I don't know enough about the redisgned Mac Pro to say anything other than that it will continue to be a processing screamer, with improved strength in its graphics processing power. Sounds like what everyone said they wanted.