The focus priority does indeed work but perhaps a bit differently from what one would expect. It does not prevent the shutter from releasing indefinitely, it simply gives a bit more time to focus.If you set continuous high you will notice the big difference between focus and release priority. In releas priority you get the full 8 frames a second regardless of focus whereas with focus priority you still get the 8FPS if pointed at something still whereas if you move the camera around randomly while shooting the FPS will slow down a lot, to about 2FPS or less.
In other words although it is focus priortiy it actualy imposes a sort of deadline, which seems to be about a half or third of a second, after which it will fire anyway, focus or not.
I think there is a good reason behind this and wouldn't want it to be different. Sometimes you don't want to miss a shot, even if it isn't perfectly in focus and the most frustrating thing that can happen is to have the camera refusing to release the shutter no matter how hard you press it making you lose that once in a lifetime shot. The way they implemented seesm to me a good compromise between the two extremes.
Now that's an idea, maybe they should make a three stage shutter button where the last stage, which you would need to press very hard, would override any of the other priorities and fire no matter what. Perhaps I shouldn't have mentioned it here and applied for a patent instead,