In my experience you need at least 8k per eye to get sharp text. But if you just want to watch a movie 4k will look very crisp and 1080p@30hz also works for movies.

So what you get is basically a larger mobile screen for watching videos, something that competes with video projectors, but you can use it on the bus. It's an easier sell compared to a device that will give you a good reading experience and competes with paper books.

Those of us that want to use them as terminal emulators are still too few.