It's more likely to happen with a complete new camera system with an interchangeable back.
The sensors will need supporting processors and DACs I guess.
It could end up something like the changeable backs on medium format cameras.
Unfortunately, this kind of goes against the flow in our 'throw away' society. Cameras, like Ipads are virtually obsolete before they hit the high street... If they made it so we could simply upgrade the sensor their profits would crumble..
But I think we are getting to a quality with digital now, where a few more million pixels won't make a lot of difference to the pictures.... This is more so on lower end cameras that use it as a selling point but still shoot through the bottom of a milk bottle. Most people are using cameras for blog, websites and on the pro front papers and magazines. Cameras have been good enough for that for a good few years.. all the race to produce the best figures on paper is really just marketing. The ergonomics of the camera is far more vital.
cheers
Gareth