I can fry an egg on my 2010 model, which was still much thicker, I really am curious to see how they manage a 300W GPU and a 150W CPU in that small space. I am also curious why they even think it's a good idea to try, instead of making the damn thing bigger, THICKER! There, I said it!
Ha!
This is really key for me. When looking for a high-end system, I want function. If you were to take all the proposed internals of the iMac Pro and build a PC system, things like cooling would be almost be the highest priority. You'd have a kick-ass CPU cooler. You'd have lots of fans carefully placed to draw hot air out and not blow it onto other components. You would have as much case space as possible to help with airflow.
Now sure, maybe the forthcoming modular Mac Pro will allow that, like any PC does, and maybe it'll also have accessibility (another priority) and replaceable components (again, like any standard system).
But this iMac Pro? It's designed to be a super-expensive desktop toy. That's why it is in Space Gray. That's why it uses the standard 27" iMac case. Sure, it looks beautiful. But you don't buy a $5k/$10k$15k system to look beautiful, unless money really is no object to you.
Now, while I want function, I do want form, and there are plenty of PC case solutions that offer outstanding aesthetics as well as function. And, indeed, with any luck that's what the modular Mac Pro will offer - a killer upgradeable rig that also looks great.
Assuming the Mac Pro is out in 2018 (although, seriously, what's taking them so long?), the life of the iMac Pro (if it is out in December) is going to be what, 6 months? Because why, oh why, would you buy one, when you could get a modular Mac Pro? They would be better off simply taking the 27" display of the iMac Pro and turning it into a standalone 5k display, in Space Grey. And maybe add a 21" option and a 32" option.
The iMac Pro seems increasingly like a concept piece that you wouldn't actually want to produce, not with a more sensible solution just around the corner. Although the fact that the modular Mac Pro is taking so long to design suggests to me that they're doing something weird with it again and we'll end up with another strange, expensive Apple compromise.
Back in the old days, that was actually fine. Mac OS kicked ass and, going back even further, the PPC systems smoked Intel. Today Mac OS is still better than Windows 10, but not by much, and computer hardware is now identical. So your return-on-investment starts to make less sense for Macs.