Two ports at once have been used for Samsung's 5120x1440 240hz monitors. Each port refreshes half of the screen and there are two scanlines going from left to right. Using the calc here you might be able to use two DP2.1 UHBR80 cables with DSC and nonstandard timings to run 4k 1000hz 10bit.
Not really? Modern hardware gets almost 1000 fps in rocket league. You don't need exactly 1000 to get a benefit, even getting 800 fps will give you a smoother experience
Here's a real-world use case where this difference is noticeable to the average person. We don't need to render video games at 1000 Hz, but many things that can be rendered with comparatively low GPU power could be made a better experience with it. The real question is whether/when the technology becomes cheap enough to be practical to use in consumer goods.
90hz is enough to prevent motion sickness in vr. That's a frame per 11ms and that's basically the limit of human perception. 120 is allegedly even better, but beyond that there's no point. Yeah we're rehashing the 30 vs 60 fps debate again but this time for reals.
I'm sure some people will demand it. But for 99.9% of the population you don't need 1000Hz content. The main benefit is that whatever framerate your content is it will not have notable delay from the display refresh rate.
For example if you are watching 60Hz video on a 100Hz monitor you will get bad frame pacing. But on a 1000Hz monitor even though it isn't perfectly divisible. the 1/3ms delay isn't perceptible.
VRR can help a lot here, but can fall apart if you have different content at different frame rates. For example a notification pops up and a frame is rendered but then your game finishes its frame and needs to wait until the next refresh cycle. Ideally the compositor would have waited for the game frame before flushing the notification but it doesn't really know how long the game will take to render the next frame.
So really you just need your GPU to be able to composite at 1000Hz, you probably don't need your game to render at 1000Hz. It isn't really going to make much difference.
Basically at this point faster refresh rates just improve frame pacing when multiple things are on screen. Much like VRR does for single sources.
Here's a big part of why they want 1000Hz. You don't need to fully re-render each frame for most cases where 1ms latency is desirable - make a 100 Hz (or even 50 Hz) background and then render a transparent layer over it.