I still wouldn't assume it to actually go further than that. It's a limitation of the EWMH standard, which is used for controlling the placement of windows.

I don't have in-depth knowledge of the standard, but I assume, it can only represent 1 desktop as the active desktop and stuff like that.
Maybe you could try to be clever by e.g. always reporting the active desktop of the active screen and stuff like that, but yeah, no idea if you can do that for all aspects of the standard, and whether applications will still behave as expected.