CUDA support is pretty critical for a lot of media production. I'm thankful that official support is here. The downside is a Mac Pro looks like a rats nest of cables with external video I/O cards, 10GbE cards, eGPus. It's a much larger physical footprint than a tower with a lot more technical troubleshooting resulting in making sure a crappy thunderbolt 2 cable is seated correctly.
Yes, external NVIDIA GPUs already work this way and will continue to do so. This announcement is about official support which only applies to a few specific configurations. The only GPUs supported are Polaris/Vega and the only Macs supported are 2016+ MBPs, 2017+ iMacs, and the iMac Pro.
