Well they'd better do it quickly, because apparently they're not doing it at the moment ...
Canon has already cut their sales forecast for this year ... twice.
So, it's not like Nikon is struggling, while Canon is riding a wave of success.
This is just the state of the DSLR market is right now.
Apparently, a saturation point has been reached and the market is stale/shrinking.
As for the rumored Nikon FF camera: it makes a lot of sense, actually.
When the D800 was released, many felt that it was not a real D700 successor - and this sentiment has not
changed with the D810 announcement.
If Nikon is smart, the rumored camera will be the D710: a D810 with a 24mp sensor and a faster frame rate.
That would be the true D700 successor and many will be buying that rather than the D810.
Same for Canon, btw.
A 5DIV with 40MP and 4-5fps frame rate will be disappointment for many 5DIII owners, who would rather see
only a modest increase in resolution - but more tangible improvements in ISO, DR, and frame rate.
Overall, one size doesn't fit all in this segment.
Some would rather have a high resolution and are OK with a slower frame rate, while others would rather have
it the other way round.
Back to the quarterly/yearly projections:
Despite lagging sales for the last two quarters (vs 2013), Canon was optimistic for the overall yearly outlook.
That's the best indication that they will be announcing a new DSLR at Photokina, which will be contributing to
the bottom line.
The question is, will that be the 7DII or a high-resolution 5DIV?
Considering how Canon and Nikon have model/feature parity at every price level, basically,
I'd say that the latest Nikon rumors just increase the probability of a 5DIV vs a 7DII at Photokina.