I think Nikon are trying to replicate the DX range in FX to some degree. The D610 = D3300. Quite slow, and not the best AF. D750 = D5300. Tilt LCD. Now it gets a bit out of sync because all the DX line have the same sensor, and it is other features, including size/style of body, which differentiates them. The 36mp sensor has no DX equivalent, but they had to start with a relatively slow camera to have 36mp, and wait for Sony to produce 24mp sensors that were cost effective to lower the FF entry prices. Now the D810 speeds things up a bit, especially in DX crop mode, but in many ways it is no D7*** equivalent. But it took Nikon awhile to get the DX range sorted, D40, D40X, D60, D80 D90! They were able to get some clear order when they went to the D**** naming convention. Naming as always been a problem though. Why start the lower FF camera (up to now at D6**? D500 would have given them a bit of room. Mention of using the D400 name would have had D300/S users getting excited.
D600 > D610 seems logical, as does D800 > D810, but D700 > D750.
I know it was probably to not be seen as a direct D700 replacement but it doesn't look 'right'.
The D750 seems to be the 'Goldilocks' camera for many, whatever it is called.
Most people don't need 36mp, but then they said 10mp is enough for most people.
I think the D800E was a way of testing the market for a camera without an AA filter. As if it were just to have come out without a filter, and a lot of people would have had Moire problems, there would have been no alternative. As it was, people could compare the two, and appreciated the extra sharpness from not having the AA filter in front of the sensor, and I never heard of many Moire problems.
DX mode on the D800 gives you about 15.5Mp, not 24Mp.
You seem to be mixing up your Mp and Mb btw.