Someone needs to come out with a current high quality 400mm f5.6 prime. I would switch systems for a high quality handheld bird lens.I think that there are a lot of people interested in a new version of the 400F5.6.... I would get it....
I love my 400mm f/5.6L... Is there anything this "lot" of people need from it that it doesn't have/do?! Weather sealing, sure, but asides from that I love it's relatively light weight and small size without IS/zoom/wider aperture - coupled with the 5D3 sensor's ISO handling this thing's even incredible when losing daylight!
I guess closer focusing would be nice but that'd maybe ruin the magical optical formula!
I agree, my 400mm is a very nice lens, fun to play with it when coupled with the 2x II extender.
My 6D's ISO allows me to be less limited to the 5.6 aperture than when I was shooting with a Rebel.
Although, I still really wished I had IS, which is why I sometimes hesitate on getting a 100-400L, but other than that I love everything about prime.
I find myself not being able to do extreme panning handheld because of the lack of IS