The nice 24.2 MP sensor from Sony NEX-7 in the D3200 is going to present a challenge to Canon to come up with a competitive body at the $700 pricepoint. After the 5D III vs. D800 embarrassment (and this coming from a 5D III owner), I sure hope Canon has something good to announce, something that does not use the same old 18 MP sensor in all their cameras.
I write reviews for camera websites and spend a lot of time talking to Canon tech people for insight and insider info on their products.
There are absolutaly no crop or full frame lenses from anywhere which can outresolve 15.5 Megapixels on crop. Take that number and give a little headroom for bayer patterns and anti-aliasing reductions in resolution (15% or so) and anything more is just a ridiculous joke.
According Canon's tech guys the reason they aren't going past 18 Megapixels is because it would be useless do so. The fact that Nikon is going all the way to 24 MP is not an embarassment to Canon, far from it, if anything the joke is on Nikon releasing cameras with useless resolution. People seem to really have a hard time wrapping their head around the idea that more megapixels will not equal more resolution and more printing ability. Here's visual proof of what the difference would be between an 18 MP crop sensor interpolated to 24 MP and a 24 mp crop sensor:
Incidentally that is also a comparison between the 5D3 rendered at 36 megapixels and the D800. That is the exact difference you will see with zoom lenses between the two and the exact difference you will see with all but the best primes. The best primes top out at 28.3 megapixels and the best zooms top out around 23 megapixels. According to Canon's tech guys they are choosing to stick to the 20 MP range because there are no lenses which can deliver much more than that. In fact the whole reason for introducing a lot of the Mark II lenses (like the 16-35mm II) was so they could resolve 21 megapixels on the 1Ds Mk III and 5D3 compared to the 13 of the 5D.
In my mind though I feel that a sensor with slightly more than the max resolution of the lenses out there is reasonable. Canon should call it quits around 29 MP instead of having slightly less resolution than the lenses out there. That's what you don't want.
According to Canon they would rather focus on high ISO than eeking out the last bit of resolution.