As far as I know, Apple hasn't been directly selling/supporting new CUDA hardware since 2012, and OS updates since then have just been supporting that older, legacy hardware. Fortunately, the good folks at NVIDIA keep putting out Mac OS drivers (usually within a day or two of a n OS update) and the cards keep working fine. All our animation stations are using GTX cards of one sort or another.
I think the litmus test will be the 2019 Mac Pro. If they drop the ball with that one, then yes, the Mac as a pro multimedia production platform will be more or less dead. They seriously stumbled with the cylinder Mac Pro, and they can't afford another dud like that. It's hard to say with Apple, though; they have pulled the fat out of the fire more than once. https://www.macworld.co.uk/news/mac/new ... 9-3536364/
We've been an 80-90% Mac shop since the early 1990s, and seen a lot of ups and downs. For the most part, the Mac's longevity, low maintenance and minimal admin overhead with almost no user hand-holding has been well worth it. As a production studio, we're usually a few years behind the cutting edge, for stability and reliability reasons, but that cushion is getting thin. It's not a religion, though, and as the next round of workstation updates looms on the horizon, if we have to jump ship, we will.