I agree with smirkypants. I don't know when, but I think eventually everything will be full frame. Or maybe even some new dimension.
How large would a camera phone be with a FF sensor?? Somehow, I don't think this is the case, tiny cameras are in demand.
That would be something, if ever it came to fruition!
Back on topic:
As others have said, crop sensors play an important role in the photographer learning curve, being cheaper but otherwise similar devices, and also make perfect business sense in a product>product life-cycle. Crops will remain for a long time.
However, I do believe they will change form, at some stage. Mirrorless cameras have steadily increased in sales and price due to clever marketing and, let's face it, size and portability. What this means for APS-C dSLRs, is that they have to be a LOT better than their EVF-only counterparts.
For the most part, Olympus, Panasonic, Sony, et al. have done a monumental job of catching up to crop-frame devices. I think part of the reason for the Nikon D3200 is to trump amateurs with high-megapixel, awe-inducing figures and sway them from equally-priced mirrorless options after failing with the Nikon 1. Truth is, the D3200 still lacks a lot of the appeal of mirrorless in its size and, no offence to the Nikon designers, ugliness.
Eventually, Canon will need to do something to fight back some of the market it is set to lose. Luckily, Canon has maintained good sales, with the first generation mirrorless actually acting as a bridge to APS-C and then on to full-frame SLRs; however, this will change. How they go about this will spell the future for APS-C mirrored devices, Canon prosumer point-and-shoots, or even their amateur line more generally.. From what I can think of, they have a couple of options:
1. Decrease APS-C dSLR size and modify styling.
Pentax released the K-x in 2009 at 123x92x68mm and Canon the 500D at 126x98x65mm. These were small in dSLR terms (the smallest I am aware of with APS-C or larger), and not too different to the (much wider) Fujifilm X-Pro1 at 139.5x81.8x42.6mm. Let's be honest, dSLRs are ugly. Seriously ugly. Most crop-sensor buyers will never be professional photographers - they do it for the fun. Having a cool looking camera is part of that fun.
2. Join the dark side.
The old "if you can't beat 'em, join them" philosophy. An APS-C Canonet is already the talk of amateur camera forums the world over. If Canon invest in CMOS, throw on an EF-S mount and a hybrid EVF, and release a couple of pancakes and collapsibles, they could charge more than the rest, yet still attract the majority of market share. It would spell the death of mirrored crop-sensor devices, but at least we full-frame users would have a compact body to turn to without having to use our EF lenses in MF on something like a Sony Nex.
EDIT: WVIL at CES last year: WVIL unbelievable new camera at CES 2011