They're putting more emphasis on the GPU on those iMac Pro's, so yeah, video users definitely targeted, and could possibly be aimed at 3D game developers/VR content creators also?
Wonder how hot those things get when under load.
It's also quite a smart strategy in appearing to make the $2.5-3k models more 'affordable'.
Edit: Is it really true that you can't get to the HDD or Ram? If so that is shocking!!
I think you can do the RAM yourself (at least you can on my 2011 iMac) but to do anything else internal, you have to remove the screen with special tools. There are videos online how to do it, but I wouldn't say it's user-serviceable.