Right now, this makes the most sense if you have a previous-generation Mac Pro and are either a gamer (not the biggest segment of Mac users, we know) or run media creation apps that can take advantage of NVIDIA's added computing power. Otherwise, you're looking at decidedly unofficial solutions, such as external Thunderbolt graphics enclosures (which do appear to work) or "Hackintosh" systems using off-the-shelf PC parts.

While there's nothing official, you could see this as laying groundwork for the Mac Pro relaunch, which could come as soon as 2018. Even if Apple has no intention of shipping NVIDIA graphics with the new desktops, this should give you more choice for video cards if the stock options don't cut it.