Maybe, since Nikon and Sony share sensor development, there is now an agreement that Nikon will get the hottest and best FX sensors, while Sony, which never made great sales with their FX chip cameras, will be allowed more "space" at the top end with their APS-C chip cameras.
It may also be that Nikon intends to relegate the DX sensor size to less serious cameras for beginners and amateurs who do not have higher aspirations. Look at the lenses. Nikon has not made top quality DX equivalents to many of their best FX lenses. Why do the DX 40mm and 85mm Micro-Nikkors cost only about 60% as much as the FX 60mm and 105mm Mirco-Nikkors? At the wide end Nikon has only a 10-24mm f3.5~4.5 for DX while they have 14-24 f2.8, 16-35mm f4, and 17-35mm f2.8 for FX shooters. In the case of the long telephotos, Nikon makes nothing exclusively for DX. In the case of the fast single-focal length lenses Nikon makes almost nothing exclusively for DX. Some FX photographers use a DX body as a non-optical 1.5x tele-converter.
Nikon's new 24 Mp DX sensor, if enlarged to FX size would be approximately 56 Mp. But perhaps there would be no real point a 56 Mp FX sensor because no lens could match the sensor's resolution. The 36 Mp D800 is already forcing photographers to shoot at optimum apertures, like f4, f5.6, or f8 to get all of the resolution that sensor can capture. If that is the case, even with top quality, single focal length lenses like a 24mm f1.4 and 105mm f2.8 Micro-Nikkor, what lens is going to be able to match the resolution of a 24 Mp DX sensor? And what are the chances that you will get that 24 Mp sensor's maximum resolution quality using lenses that cost only 60% as much as the FX lenses cost?
To me, it looks like Nikon now considers DX cameras an entry system for D-SLR beginners. A stepping stone. And that when those beginners grow up and want more quality, Nikon will say that the way to get that higher quality is to move up to FX. And maybe Canon also shares that philosophy.