*These are two very different things.
Things are quite slow in regard to upcoming cameras (in terms of rumors). Basically, there is the Nikon D5 coming and that's it. The long-awaited D400 is not yet here (and, alas, maybe never), nor do we have any smaller DX cameras coming.
|The D80 was much better than the D70. The D90 was even better, and the D7000 even better. But after that, something happened...|
The first thing you need to ask yourself is this:
What would a Nikon D3500, a D5600, or a D7300 look like? In which way would it be different than the D3300, the D5500, or the D7200 respectively?
Exactly. Almost certainly the same 24MP DX sensor (or a very similar one), perhaps tweaked a bit to give a tiny bit better JPEGs. Maybe half an fps more, maybe one extra scene mode, some WiFi thingie, some other meaningless special effect, and that's it.
Consider these upgrades:
D80> D90> D7000> D7100> D7200
D3000> D3100> D3200> D3300
D5000> D5100> D5200> D5300> D5500
(or, if you want to examine things on the top of the heap):
D1x> D2x > D3(x)> D4
Do you see the pattern here? Every newer upgrade was less groundbreaking than the previous one. Indeed, I challenge you to find one (1) photographically meaningful improvement between, say, the D3300 and the D3200, or the D5500 and the D5300.
Which brings us back to the situation today. It's very probable (in fact it is virtually certain), that we'll get a Nikon D3500 or a D5600 sometime soon. The real question you should be asking yourself, then, is this: who cares?
If your photography leaves you in some way unsatisfied, you must first identify the problem. You (the user/photographer) are the culprit in 95% of the occasions. This has nothing to do with ability or experience, by the way; it's the case for all of us. This is good news, however! You can fix it for free. No new camera, no new lenses. Just work with your dissatisfaction. If you don't like your low light photos, the answer is not a camera with an ISO of 102.400. I'm using the D3200 with the kit lens in any light and I have no issues. If I did, I'd use a faster lens - like the cheap and excellent Nikkor AFS 35mm f/1.8
To sum this up: if you need a new camera, chances are you will be disappointed. Only a D400 (a D7200 in a D300-style body; or a D300 with a modern 24MP sensor) would be a camera I'd consider right now. Unless Nikon surprises us with something truly revolutionary in terms of making photos (which I sadly doubt), a D5500 is not really that different than a D5300, and so on.