...be worth it as well if they can maintain a constant f/4.
You realize how nutty that request is? It would be bigger (and more expensive) than the 200-400/4.
Ummm, Oooook, I was being.....facetious ?? attempting humour ?? it's an Aussie thing.
I understand on CR that sometimes, as in this case, doesn't work, I'll endeavour in future to be more serious, more in line with all the other very serious viewpoints that get Posted on CR from time to time, in among the more serious viewpoints, naturally.
And on a more semi serious note, a 100-400f/4 Lens with the IQ of the 200-400f/4, shouldn't be any larger, or more expensive than the attached, seems like a Bargain at $27k, well, except for the cost of the 2 Sherpas you would need to cart the thing around for you.