Early on in yesterday's WWDC keynote, Apple announced VR support in OS X, along with an external GPU dock for Mac developers. That news excited a lot of people.
External GPUs, for what it's worth, work right now in macOS Sierra without huge issues (Bizon has been selling external GPU enclosures for a while). What Apple's new High Sierra OS brings is full support for GPU docks in its graphics API. Couple that with NVIDIA's commitment to release graphics drivers for macOS and it's suddenly going to be a lot easier for Apple users to boost the power of their machines.
Immediately after Apple's VR announcement, a colleague remarked that adding an external GPU would be "dope if you're buying a MacBook Air or a low-powered machine" -- you'd have an ultraportable that you plug into a dock for VR and high-end gaming. That dream isn't realistic though. It feels like many people don't quite understand what a GPU does and why adding one to an underpowered machine won't make it VR ready.