Originally posted by Rondec I have no idea. But the D750 was announced in September of 2014, while the D610 was announced October of 2013. I am sure new sales of both are lagging as they are pretty long in the tooth. I agree that it would make sense to give the D620 (or whatever they call it) specs that are at least as good as the current D750 and a few added features (4K video, improved AF module).
I always got the impression that the D750 was a slightly more expensive D610 with beefed up frame rate for folks who were sports shooters but couldn't afford D5s or cameras like that.
Sales are still brisk for the D750.. they keep selling out. I see 'more on the way' on B&H and Adorama fairly regularly.. I've kind of been watching for the past few months
intensely.
The D750 has a much improved AF system, flip screen, higher resolution on the LCD screen, slightly faster burst, better battery life.. over the D610.
They currently have a situation where if they update the D610, they wind up giving it features the D750 already haves. That means they either discontinue the D750 or also update it too to keep the positioning similar. I don't think 4k is going to be enough to convince photographers to go with a D620 over a D750, yet the only way to really improve a D610 is to give it what the D750 already has. Tough spot.
And since they seem to be tight on funds these days, I think they end up discontinuing the D610, milking the D750 and then updating that when the time comes (hopefully sooner than later).
I've read (rumor obviously since it isn't out yet) that Nikon intends on selling the D810 alongside the D850. So I think the D810 takes the D750's tier and the D750 takes the D610's tier, provided that rumor is correct.