True...but what if it was lighter than the 600 II? 600/4 = 150mm front element, 800/5.6 = 143mm front element...so lighter is possible.
Also, I think they need to update the 800/5.6 for optical performance. Those who do their research (which I would hope is almost anyone spending $13K on a lens) pretty easliy learn that the bare 600 II is optically better than the 800/5.6, enough better that you can add a TC and it's still better. The 600 II + 1.4xIII is better than the bare 800/5.6, plus it's 40mm longer, lighter and cheaper, and offers f/4 when you use it without the TC. The 600 II + 2xIII is optically better than the 800/5.6 + 1.4xIII, too, and likewise it's longer, lighter, and cheaper. So, with the 600 II performance, I see no real need for the continued existence of the current 800/5.6.