Even if they aren't closely tied to the X software package anymore, they are literally called "the X.Org Foundation". Why wouldn't they want to hang on to x.org?
I've seen posts by "X.Org Foundation" on their official Google+ page to the effect that Wayland is the display server of the future and efforts should be focused to target it.
Since X is now deprecated tech (the foundation itself even states that Wayland is the future), a name change is perhaps in order.