Which is odd, because X11 has all this visual and depth stuff leftover from the days of 1/4/8/16-bit displays, and mixing windows of each type on the same screen. You would expect it to be capable of representing 48 bits just as well.

I wouldn't say its "plain impossible" with X11, but its significantly easier on Wayland because its a far simpler design that aligns better with the graphics hardware, we're sending surfaces (or pointers to them) with metadata to the compositor, not drawing APIs.

That already works with Plasma Wayland. It's still a bit finicky to make it work with things running in XWayland (Windows games primarily) but it's getting better.