Larry, you obviously do not have a need for a computer this powerful (and the resulting cost) and that is totally 100% cool, but there are people that do need a computer this powerful and are more than willing to pay for the benefits it brings.
I'm just one example of a wide-array of people that need powerful computers, but allow me to explain why I "need" a computer like the iMac Pro or possibly the upcoming Mac Pro that may be released sometime in the next year or so. I am a full-time photographer and video producer. The work I do is my main source of income. What I produce is literally what puts the roof over my head and the food in my mouth.
Compared to my late-2014 iMac (in my sig below), the iMac Pro will shave a TON of time off my editing work. On the days that I spend in my editing studio, the iMac Pro will easily shave an hour and a half or more off my day. That is time that is freed up so I can complete additional work that I am being paid for.
Furthermore, it's not just the increase in speed that comes from specific one-time tasks such as a large transcode, it is also the ability to smoothly flow through cutting and editing 8K video and multi-cam 4K. The advantage to this cannot be stated enough. When I am able to flow smoothly through the editing process without hiccups, dropped frames, or interruptions, then my creativity can better emerge and I am even more likely to produce a better product. Remember, the desire for someone to hire me for their next project hinges on just how good my work is.
Hopefully this gives you some insight as to how and why some people need a computer as powerful as an iMac Pro and why we are willing to pay so much for it. It's all about utilizing the right tool for the right job.
Well, you're just full of "obvious" assumptions, and most of them are wrong.
"a computer this powerful"? It's an iMac, not Excalibur. The iMac Pro is the most powerful Mac ever built (that distinction has been tossed out so many times that it has ceased to be anything other than a banal marketing term), but it's not that much more powerful than it's predecessors. "Space Gray" doesn't make it any faster.
The base model looks to benchmark about 25% faster than a 5K iMac. Yes, it has enhancements those benchmarks may not show, but it has no track record for reliability, an important concern in professional workflows. I would never rely on an untested model to meet deadlines, nor would I ever depend on a single workstation. Can you light up all the cores and run the iMac Pro 24/7 for weeks at a time? You'll find out. It's certainly something I'd feel comfortable asking an oMP to do, and I have on many occasions (I would not ask an nMP to do it without having a fire extinguisher and adult supervision handy).
You're not the only person earning a living from your Macs, or willing to spend money on a professional workstation, I find the base model iMac Pro priced fairly, it's only when you start adding all the buzzers and whistles that it becomes an homage to Apple's margins.
I spent over $13K on a MacIIfx in the early '90s, the equivalent of over $21K in 2017 dollars. While it was the "Fastest Macintosh ever built" and about 25% faster than the next fastest model at the time, it probably had less processing power than the current Apple Watch, but it served its purpose and gave me a competitive edge at the time. I've never scrimped on Tech, but I'm not willing to just throw money at Apple because they insist I should.
Photography, on any professional level, is certainly not beyond the reach of most modern Macs, although I've never been a fan of AIOs for that task. As for video, I never found it a compelling task (are you really suffering from all the issues you mention on your current machine?) and I recently tossed my old copies of Final Cut Pro, (I did keep my copy of Pre-Adobe, Cosa After Effects for old time's sake. Now that was an impressive product for its time).
If you want an iMacPro so badly, they're trickling into Apple stores right now (Santa Monica has them); sadly, just base 32Gig models, but if you need a $5K write-off for the year-end and haven't pre-ordered, it's a thought. I know I considered it for the better part of a second before I discarded the idea.
