It'll need to be.
I wonder what the content will be, is there really much "3D" content? I guess that's coming, but right now?
I also wonder what the effect of watching "3D" content for many hours will be. Now I know the world is "3D" but the world isn't "fixed focus", the unnatural part of watching "3D" content is that the viewer must fix their focus on the display, even though much of what they are viewing suggests otherwise. Additionally "fuzzy focus" in the scene (like when you look over someone's shoulder at the part of the scene the director wants you to look at) is really confusing for the brain (the foreground "fuzzy" part of the scene cannot be brought into focus). I imagine if the viewer watched large amounts of it they'd suffer headaches. While it might seem quite natural, it really isn't.
I also think Sky are going to find it hard to tempt people into paying EVEN MORE. If HD was a hard sell, this is going to be really difficult.