Upload & Sell: On
I think what I'd prefer is a lens that Whayne proposed a couple of years ago - a 125-500, maybe f/4.5-5.6 like the current 100-400. Maybe even 1/3 stop faster, f/4-5. Using latest construction to keep weight reasonable, a fluorine coated front element, etc. Even for 3 or 4 thousand bucks it would be a bargain, and I'd find it more useful and usable than the 200-400 with converter.
Well, I can see such hypothetical 500mm zoom developing its following, however, Canon have decided on the 200-400 (560) f/4 (f/5.6) mm option, so it's a done deal now. They must have given it some careful thought, not only based on the Nikon's experience with 200-400 VR, but also doing the analysis of Canon's own customer base etc.