But there are safety concerns, and it's not possible to go 1000km/h on the highway. So there's not much point in having a 1000km/h car, because you will never use its full potential. Just like a 1khz display (supposedly).

The analogy is strained and no longer applicable. Sure, you won't be running Cyberpunk 2077 at 1 kHz, but you'll use a 1 kHz display to its full potential of imperceptible latency and eliminated motion blur in regular desktop use, with every movement of your mouse and scroll of its wheel.

Even in gaming, less demanding games can hit 1000 Hz and console emulators will benefit from reduced latency too; you could actually beat CRT latency.

Well, maybe I'm biased - I've tested a 120Hz monitor recently and I legitimately didn't see a huge difference between 60Hz. Maybe in mouse trails when I was intentionally looking for the difference. I can't imagine how insignificant the change to 1Khz would be for me. But I'm not a gamer and I've spent my whole life on screens like this, so maybe I'm just blind and other people are much more sensitive to this - in this case I agree my analogy doesn't make sense.

The cost I guess

Sure, but the cost only applies to people who want the feature, so it's fine, right? I'll buy the 1 kHz monitor and you can buy the 60 Hz one.

That's an obvious downside, though one usually easiest to figure out with economies of scale.

OTOH, it's freaking hard to figure out safety at even 100km/h.