With good lenses and good light, a camera remains as relevant as the it was the day it was introduced, assuming the sensor is able to produce an image suited for the purpose. This includes my 7D, 40D, and, to drift off-topic a bit, my 5D. (The 5D, if I recall correctly, was announced in the second half of 2005, so is a design that is 12+ years old.) I see no reason why my pair of 7D II cameras will be any different. If anything, the 7D2 cameras will remain relevant longer, because of their ability to detect flickering light, and synchronize the shutter, producing uniform exposures and WB, in places where that is a factor. For some shooters, this feature, alone, was a game-changer.
A 7D Mark III may or may not be a significant improvement. There is simply no way to know, in advance, how this will affect the desirability of owning a 7D Mark II. The 6D II was a disappointment, for some, which has probably preserved some of the original 6D’s “staying power.”
The Nikon D500* has “stolen” some of the 7D II’s “thunder,” so it will be interesting to see the long-term effects. Canon’s response to the Nikkor 200-500mm lens, if any, may be a significant factor in this equation; some number of bird/wildlife photographers really favor the D500/200-500mm combination, in spite of the 200-500mm not having the AF speed of Nikon’s higher-level super-telephoto lenses. The 200-500mm was built to a price, and its price seems to have caused many buyers to act. (I would rather be patient, save, and pay more, to get faster AF, a wider maximum aperture, a more-secure hood, and better build quality.)
*We have his-and-hers D500 cameras, for me to use as a reference point, but I still love my 7D II cameras, and they still have plenty of work to do.
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I wear a badge and pistol, and make evidentiary images at night, which incorporates elements of portrait, macro, still life, landscape, architecture, and PJ. I enjoy using both Canons and Nikons.
