Although this is good news for pro Mac users it's still not that meaningful in an age were CUDA still dominates for almost anything you'd want to use this power for in an iMac (You're not going to want to mine ETH or compute ML inside an iMac chassis so I'm thinking more visual work).

Speaking as someone from the creative professional side I waited and waited for OpenCL to take off I thought a year after the trashcan pro with it's dedicated compute GPU (only one of the two GPUs was for display the other was 100% OpenCL) then nothing, I waited two years then nothing, etc. Then eventually I caved and moved to PC just for the Nvidia like most of people in my industry [1] [2] [3]

3D and motion graphics people are leading the way with this but look into the tech Adobe is prototyping and the future of photo manipulation via ML, within the next 5 to 10 years multiple GPUs as purely compute units will be essential for many creative professionals.

[1] http://rawandrendered.com/Octane-Render-Hepta-GPU-Build

[2] http://www.yambo.me/blog/2016/4/4/watercooled-4x-980ti-octan...

[3] http://www.mattfrodsham.com/octane/2015/4/10/4xgpu-pc