How the new Mac Pro was designed....
That isn't their problem. On the PC side the people who make heavy upgrades just start with after market cases. There's no reason to buy from an oem in that situation. Oems also use a lot of proprietary sizing to interrupt that. Sometimes it's a custom size for a power supply or board or whatever. They want to push all in ones more to guarantee a higher minimum sale and reduce the number of parts they must validate in a given year. High fixed costs dedicated to validating parts, an enormous matrix of cto options, MS licensing fees, and not enough differentiation in brand perception have caused a lot of problems. They're commodity units. IBM had that concern years ago when they still held a high level of product differentiation with the Thinkpad line. They got out of that market. I will say Apple's bet on the phone market was a very smart one. Perhaps that's an understatement. Anyone should have seen it coming with Handspring, Palm and later Blackberry. None of those had the same level of adoption though.
It's not entirely practical for everything. The solution isn't to add external pci. It's to provide similar functionality from the base hardware whenever possible. If anything is external, it should be sold that way. So far not enough stuff has shown up, and it still has to pass intel's certification process. I would be more into it if it was an open standard and something widely adopted. Higher bandwidth will come eventually. It's not so much in the form of thunderbolt 2. Thunderbolt 2 seems to allow for channel bonding. It's not a real bandwidth increase. Combining that functionality with increased bandwidth could allow for more interesting solutions. It would still cover a lot of storage stuff today if more solutions show up. As of right now everything is still quite expensive compared to alternatives. Some are acceptable to me personally, so I'll probably end up with one.
It depends how it's allocated when shared with displays. A lot of what I dislike is relevant today, but at some point it will be good enough. In terms of general success, it's a matter of if it adds value for the majority of users where it appears. They dropped the express card slot because no one used it. I used it a bit on my notebook, but admittedly Mac support was terrible on those cards. I'm not sad to see it gone, although I would have liked to see 2 ports from the start to alleviate contention and a few more peripherals. I don't buy into the idea that the mac pro is what will bring volume up and prices down. They ship way more of the other machine. What it's likely to do is eventually motivate more vendors of specialized hardware to release breakout box form factors. Black Magic was one of the first to do so. Most of theirs run on usb3 or thunderbolt.