There are pro apps out there (e.g. Lumion) that have not and will not port to Mac because traditionally the graphics was too weak. Perhaps now with the iMac Pro (and modular MacPro coming in '18) and the ability to use eGPUs, that may change.
Once Intel announces their new Xeon Purley lineup on July 11th, we should know what actual Xeons Apple will be using in the iMac Pro. And the list prices.