Roland Vink's site says about 370 have been manufactured but the number should be more (at least 1,600 copies by now), mine is 2016xx (2014) so that one guy in Sendai busy with assembling them seems to complete them at about a pace of 1 per day
Given the price and (more importantly) focal length, this isn't a lens that will appeal to large numbers. Those who do invest in it will however notice that it delivers quality in all areas, most importantly detail and reach. This is a perfect lens for shy animals or any other situation where physical reach is mandatory to get interesting frames. The field-flattening effect of 800mm is wild, and even 400mm veterans need some time to learn to use it for compositions. Naturally, it blurs just about everything behind the point of focus. I have not used it for sports, as I have had no interest to enter that market - the focusing speed should however easily match the requirements of motorsports or fast-paced players. This isn't a very practical lens, but for birdlife it is very interesting. I spent some time during my short summer vacation photographing birds with it and it certainly allows a less experienced "bird sneaker" like me to approach subjects to interesting distances.
The square crop bear faces are from May 2013, when I was trying out the lens for the first time. I am not an experienced wildlife photographer, as a matter of fact those photos are from my first encounter with bears in the wild. The last photo (mosquito in front of bear face) is a 100% crop of the 2nd last photo.
EXIF:
46697 - D4 800mm f/5.6 1/640s ISO 12,800
47902 - D4 800mm f/5.6 1/640s ISO 3,200
47908 - D4 800mm f/5.6 1/1600s ISO 3,200
48227 - D4 800mm f/5.6 1/400s ISO 450
48486 - D4 800mm f/5.6 1/160s ISO 12,800
46919 - D4 800mm f/5.6 1/200s ISO 3,600
48216 - D4 800mm f/5.6 1/400s ISO 5,000
48551 - D4 800mm f/6.3 1/400s ISO 10,000
48641 - D4 800mm f/6.3 1/320s ISO 12,800
48641B - 100% crop of the previous (48641)
Some 800 + TC photos to come...