At this point, it seems pretty difficult to justify the 50% premium of the 80-400; Nanocrystal coating and perhaps a slight edge in AF speed seem to be the only real benefits aside from the different range of course. Or am I missing something?
Zooming is much faster on the 80-400, with the 200-500 it's quite a slow process. This is quite significant in action scenarios, e.g., an airshow where you'd want to frame to compose the plane(s) and the clouds as things happen; with the 200-500, zooming takes a while and it's just not something you do on the fly. It takes me 6 seconds to zoom from 500mm to 200mm, and 8 seconds to go from 200mm back to 500mm (using the left hand to zoom with the lens in shooting position). With the 70-200/4, either way just takes 1 second. I think for formations I would use a 70-200mm, and regard the 200-500mm as an adjustable prime lens pre-set to 400mm or 500mm for those long shots.
The 80-400 offers a more convenient (and available!) 77mm filter size (vs. 95mm), nano coating, AF that works also at close distances (the 200-500 often needs manual help at close distances), a 5x focal range, and is more portable and hand-holdable. The 200-500 is sharper at f/5.6 and offers the 500mm focal length, and perhaps is a bit better constructed (but this comes with the tradeoff of glacial zooming).
I guess for landscape photography the zooming is not at all a problem, but I thought I would be able to maintain approximately constant framing on an approaching subject in some sports scenarios and this is just not possible with the 200-500mm. For me this is the main limitation of the 200-500. However, not having a sharp f/5.6 is a more severe limitation for me, so my choice between the 80-400 and 200-500 sides with the latter (the fact that I already have the 70-200mm range covered with a fast, high-quality zoom contributes to it). For someone who is ok with stopping down a bit, and needs quick access to a 5x zoom range, the 80-400 likely is the better choice.