Nikon needs to dump the D750 quickly. Redesign, correct the flaws - throw in a few small tweaks and upgrades since time has elapsed since the original release date - and call it the D760.
History repeats itself, D600 to D610
At least Nikon is honest and upfront about the issues, and fixes them without hassle. Some companies deny, sweep it under the rug, then if they have to make it right, give customers a hard time.
Just bizarre the D600 and D750 have had all these issues, but as far as I'm aware, the D810 has been solid. Do they have separate teams engineering these two body types or something? Different origin of manufacture perhaps?
Whatever, that's their business. My 5D3 and 6D are troublefree.