As I said yesterday, a 500mm f5.6, f6.3 or even f7.1 DO, for use with extenders would make more sense. Although I can see a use for this. With my type of photography, you could shoot perched birds with it, and anything much wider aperture at 800mm is going to be pretty big and expensive. Although I'm a bit puzzled about f11 at 600mm, because I'd have thought you could make it f8, and it would still be possible to make it a fairly compact and relatively expensive lens, given that f6.3 600mm zooms aren't massive.
You have to think the aim is to make these lenses very compact. My first thought when seeing the parameters is that these would be mirror lenses. If they're DO lenses, then Canon must have got the manufacturing costs down, or I can't see the point as these would be too expensive. If a long lens is f11 wide open, there will be very little need to stop the lens down.
Yes, these maximum apertures are going to be a bit limiting to say the least. To use any sort of fast shutter speed to capture action you're going to have to use pretty high ISOs, even in bright light. Anything more than a clear sunny day and you're going to have to use very high ISOs for any sort of higher shutter speed. A large proportion of long lens photography is of action, with only landscapes and stationary wildlife being contexts where you can use slower shutter speeds.