I currently have an iMac and was looking at upgrading to the next Mac Pro (if it ever will exist) but i'm not so sure anymore, since i would use the horsepower mostly for encoding and rendering it would be much better to buy a dual socket workstation from HP or Dell (or build my own), for some workloads the Mac Pro is so out of touch/sync with the market.
I hate the design of the iMac though, there is probably alot of people that would want Apple to get rid of the chin (personally i would like to mount the iMac on a VESA mount so i can use it in both portrait and landscape, current iMac with its chin + multiple monitors, yeah it sucks), a 3 monitor setup with an iMac and 2 5K Apple monitors would be awesome if they had a very similar front design and a superslim bezel
http://www.yankodesign.com/2016/09/28/imac-is-getting-all-touchy-feely/
But, since our favorite CEO is at the helm at Apple this future is pretty much an impossibility