Canon have been working on high MP sensors for years! I was told by a Canon representative that a 50MP was being tested some 5 years ago so it's only natural that the 'trade' will all be working on something that's leaps ahead in terms of pixel count as this always stimulates sales.
I don't think they are aimed at the amateur market just yet, may be military or astronomy etc to start off with but one thing I am sure about is companies will need to make lenses which will resolve the extra pixels and there will be no point putting anything but a L or equivalent lens on the front of a high MP camera!!