The recently announced iMac Pro is a beast of a machine. That said, it seems like a very niche model that won’t move Apple’s revenue needle in any appreciable way. While the machine is geared for professional graphics users, I don’t foresee most graphics/CGI shops buying these. For one, companies would expect to get many years of life out of an expensive workstation. In this case, a non-upgradable machine might go two years before its specs start to feel outdated. (This is especially true of the GPU, where there are regular large performance improvements. One could presumably use an external GPU, but that defeats the purpose of an all-in-one.) If the iMac Pro offers target display mode, then at least you’d be left with a very nice monitor. But Apple hasn’t given any indication that TDM is coming.
I see the iMac Pro as a bragging rights computer. Apple gets to brag that it offers the most powerful all-in-one on the planet and flush buyers get to brag to their friends about their purchase. But for the graphics professional, a revamped modular Mac Pro would make a lot more economic sense.