We had a discussion here at PF if full frame is a niche market (too small for Pentax actually), or not.
In this respect, it may be worthwhile to notice that Nikon Germany has just published a press release entitled:
"Volles Format. Alle Möglichkeiten – Nikon mit Fokus auf FX-Vollformat-Fotografie" (engl.: Full Frame. All Possibilities -- Nikon with focus on FX full frame photography)
The full text is published here:
Nikon setzt voll aufs Kleinbildformat | photoscala
It basically announces that future Nikon sales and marketing activities in Germany will be focused on FX.
The announcement incudes a URL, currently under construction:
http://www.nikon-vollformat.de
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My personal take at this is that camera sales have come under serious pressure over the last year or so and that full frame emerged as a segment being somewhat immune.
Moreover, I think this pretty much rules out any possibility Nikon would deploy a DX-size D400 any time soon. This should be good news for the K-3, however I see 7D and D300s users post about K-3 missing selection of 500-800 mm glass, TCs and possibly inferior 3D tracking AF.
So, it may well be that between smart phones and full frame, pretty much everything else is collapsing right now.
Maybe, it is just that the fashion trend for digital cameras incl. dSLRs which grew for 10 years now comes to an end, leaving the photography industry where it started off in the late 90s. Not the worst thing if you ask me. And it makes DX synonym to this fashion trend, at least for Nikon.
In the end, the 35mm format may not be as niche anymore as it used to be for the last 10 years. Partly because of shrinking APSC SLR and shrinking mirrorless system camera sales.