I haven't figured out the Wayland solution yet, but on X11 you can use a tool called Devil's Pie to make Stellarium act as your desktop background, which is way more fun than any other desktop I've had: http://mooooo.ooo/stellarium-desktop/
I think the DE compositors should have an option to launch an application as background - full screen, always on the bottom. Wallpaper would just be an instance of an image viewer run this way. Animated wallpapers could just be ffmpeg or VLC playing a loop.
Demanding enough that I’d kill it before doing any gaming to get a small boost in FPS, but otherwise, when you aren’t interacting with it I think cpu usage was something like 3% on my i5 processor. When you’re moving around the view and such though, it does use a significant amount of cpu.