Incorporating an extender into those lenses would be great, as the optics are matched to the particular lens (that is how the 200-400 is). However, every big white is pretty new, including the 800, so maybe for the next refresh? It would be cool if they built in a 1.4, and then gave you a 1.6 external extender that is also optically matched to the lens so if you still need the 2x, then you would add that extra .6 the traditional way. It would probably add $1,000-1,200 to the price of the lens, but it would be a great innovation in my opinion.