I'd imagine if you were going to invest in a 4K projector you'd still want a drop down screen unless your walls are perfectly flat white and non-textured.

Definitely agree it would be nice to have a hidden TV though :)

Or just have a huge TV that's flat enough to act as art. I think most TV manufacturers include some sort of "art" mode where it just shows a photo or slideshow. Heck, all of the streaming boxes do it.

I don't know of any eInk displays that could function as TVs, and a TV in "art mode" will end up putting out a lot of backlight, which is basically the opposite of what you'd want when you're trying to hide your TV.

You really need a screen for a projector, even the flattest white walls have some kind of texture that is prominent enough to degrade the image. Luckily screens can be had for quite cheap, at least in comparison to the cost of the projector itself.

But also, if you want high-quality surround sound, then the center speaker needs to be at ear height in front of you. The way home cinema owners arrange that is by putting the speaker behind a screen that has tiny perforations to let the sound through.