> HDR...

Yep. Sucks. It's the only thing I miss about gaming on Windows. Hopefully xlibre will be adding that in.

> ...VRR, Mixed refresh rate/DPI displays, Zero-copy video acceleration...

I know that the first two work fine on xorg [0]. It's not entirely clear what you're talking about with the third, but I know that xorg supports compositor bypass for windows so that programs can interact with the graphics card without the windowing system getting in the way. Like, I think this is a thing people were talking about working on back when Compiz and its wobbly windows was new and exciting.

If that isn't what you mean by your third thing, perhaps you'd be interested in specifying what video acceleration mechanism xorg doesn't have?

> ...support for tiled GPUs.

Doesn't that only matter for Apple Silicon(TM) machines, and maybe some ARM machines with integrated graphics? If folks want that, it's "just" a matter of writing the drivers to make it happen and getting them into an xorg fork. Can you show me a feature or features of xorg that makes it impossible.. other than FDO's tactical neglect?

EDIT: Actually, I dimly recall some old hardware that I think was supported by DRM that did tiled rendering. Maybe it was some PowerVR stuff? If my memory isn't failing me, then there's the counter to claims that it's impossible for xorg to support. :P

[0] Source: Me having these work just fine for quite a long time now on my personal machines that run xorg.