Nikon is really aggressive with new cameras releases.
Not really.
D3300 - scheduled release
D5300 - scheduled release
D7100 - scheduled release
D400/D9300/whatever - still MIA
D610 - quick fix of the D600
D750 - scheduled release (if you consider it the successor of the D600 and view the D610 as just a quick fix)
Df - only camera that actually was NEW
D800 - well lets interpret this as successor of the D700. Which otherwise would also be MIA.
D810 - scheduled release
D4s - scheduled release
Thus, except for the Df and the D610, all of these new cameras have been kind of expected around this timeslot. The D610 was just an attempt to fix an obvious problem with the D600, the Df was a halfcooked attempt to do a retro camera.
The only real surprise really was the D800, which indeed was a gamechanger.
The strategy around the canceleing (or removal) of the Anti Aliasing Filter and the Optical Low Pass Filter has also being doing a sharpness revolution in itself.
I would call this a trend, not a "revolution", plus that wasnt started by Nikon, in fact they came late to the party and neither the D800, D610, D750, Df nor the D4s have this one. And the first camera that had it, the D800E, came at a hefty additional price.
Camera sensors wont be sharp until somebody manages a Foveon sensor without the disadvantages of high noise and thus bad high ISO performance. No AA filter is an improvement, but not the final solution.
The growing of ISO performace [...]
Normal for everybody except Canon. Also, the additional gains in this area are decreasing. A D700 already had pretty good high ISO, and the old D3s is still one of the best performing high ISO cameras.
For me (not a sports photog), the native base ISO 64 at the D810 is also revolutionary (again) these days.
Thats again just a trend. The D750 doesnt have it as well. Digital medium format has it since ages.
Revolution, that was for example autofocus, or image stabilization. Neither Canon nor Nikon manage to give their DSLRs a sensor based image stabilization, though. So its only available with them if you have glas that can do it.
That's a lot. Most of these lenses are really shining in the reviews out there
Overall Nikon and Canon do great lenses, yes. A couple other companies with less luck do as well - Olympus, Fuji, and of course Leica and Zeiss. Of course everybody produces stinkers and great glas - but for some companies thats a lot less stinkers and for others theres more of them.
But I am not aware Nikon is more active than before. A lot of lenses are still awaited since ages, like an AF-S 135mm f2 or f1.8, or a PC-E 17mm. Other lenses are disappointing, such as the new 58mm f1.4.
Also, Nikon still has little to nothing in respect to higher quality Nikon DX glas, and DX wideangle lenses are still prohibitively expensive. Want to get good wide angle with Nikon ? Then you have to invest into a FX camera.
What do you think of 2015 onwards?
Maybe finally somebody will release a mirrorless system, other than the Leica M, with really high quality. Sony already did a very good attempt with the A7s. Unfortunately these cameras are still Sony - its not a photography company, and unfortunately it shows in their products. Meaning Sony E and FE still lack in respect to glas - both in respect to quality and choices.