For one, you can't really make lenses any smaller than they are, and in some cases, you also can't bring them any closer to the focal plane (think about any f/1.2 lenses - light is already striking the sensor from such an oblique angle that there are problems with the amount of light which the sensor "sees").
The overall body/lens package needs to be balanced - current "pro" bodies are "about the right size" to use with a lens like a 70-200 f/2.8.
It would also be difficult to pack all the controls you need on a pro body into anything much smaller without compromising ergonomics.
I agree. A p/s camera with tiny lenses is very different to hold than a camera with a decent sized chunk of glass.... And the "big whites" are another thing altogether. You need the size for balance, a good grip, and access to a reasonable number of controls. For example, the big difference between a 60D and a rebel is the shoulder display and controls... It makes it a far easier camera to use, plus the larger body is easier to hold(at least for me). Shrink the size too much and you loose functionality.
I agree. Unless there is a major technological breakthrough in the field of optics, lenses can't get much if any smaller. A big lens will need a good sized body to balance it.
I also agree that the currenty DSLR bodies feel right in my hands. I have a 6D and 7D and both feel good and are easy to operate. I used to own a 550D (T2i) and it was a little to small for me. I've handled an SL1 at a store and while I like the small size, I would not purchase one for me, as its just not comfortable to use for an extended period. For my wife, its a very nice size however.
I have a S100 P&S that I carry at times when an DSLR isn't an option or I just don't want to lug heavy equipment around. It takes decent pictures, but I would never be satisfied with it as a primary or only camera.
That said, none of us can predict the future and I'm sure there will be technological advances that none of us can anticipate now. So, lets see what unfolds in the world of photography equipment, I'm sure it will be an interesting ride.