wow.....
That's gutsy. I hope you can upgrade the graphics else in 3 years that's going to be quite out of date (unlike the 6+ year old monitors I have doing sterling work, the oldest having fared my last 3 graphics cards.)
Apple will reportedly build GPU chips directly into its next line of monitors. Apparently, the Cupertino idiot-tax operation will soon unveil a new Thunderbolt 5K Display model that will sport its own graphics processing hardware. It's whispered that the new monitor will not be unveiled at the upcoming Apple Worldwide …
That's the point, lIke SmartTVs, the whole purpose is to obsolete the display before it's time forcing people to buy new. I have 15 year old displays that work fine with whatever input happens to be connected. Granted they're tiny by today's standards, but fit the almost-headless server role very nicely.
I wouldn't dream of trying to use a 15 year old graphics card in a modern PC (not that it'd fit anyway).
I doubt the intent is that the GPU in your PC is not used, just that it provides a different path - obviously the "GPU in monitor" would require a different protocol that passes graphics primitives to the monitor instead of raw HDMI data. Passing raw HDMI data that has already been rendered will still be supported.
Given that display chips are becoming more complex with stuff like built in scalers, going with a full GPU doesn't add much cost...certainly such cost is lost in the noise for what Apple is going to charge for a 5K monitor.
I wouldn't count on support for such a scheme outside of the Apple ecosystem, so it probably won't help you with a Windows PC, and almost certain not with a Linux PC. Kind of hard to see what the plan for this is, since I really doubt Apple is going to start selling PCs without a GPU intending that it is built into the monitor. Maybe it is intended for wireless use, since it is damn certain that you aren't going to deliver 5Kp120 12bpp wirelessly, but if you used primitives and had the monitor render it, it becomes quite doable.
AIUI the thunderbolt connection currently available wouldn't be fast enough to shift 5k's worth of graphics data. Apple solution? Shift the graphics card to the monitor to reduce the data bandwidth requirement between computer and monitor.
http://www.macrumors.com/2016/06/01/5k-thunderbolt-display-integrated-gpu-possible/
Downside is that if the monitor only has a thunderbolt connection (i.e. no HDMI etc) which obsoletes the monitor with the graphics card that isn't good. That said - Apple tend to flog iMacs and MacBook portables that have similar problems when it comes to a graphics card that can't be upgraded.