Interesting post on dpreview from someone who talked to the Sony Alpha 900 team at PhotoPlus last week:
"They claim that they convinced the sensor division at Sony (the folks at PhotoPlus were camera designers) NOT to sell the A900 sensor to anyone, in order to build Sony's camera market share."
Canon has been doing this for years. This basically means that Nikon may not have a choice of sensors beyond 12 MP and their only way up is to go medium format (MF sensors are not restricted to a certain manufacturer). There is a dark area of who exactly produces the D3 sensor, but it seems that Nikon may not be getting the latest 24 MP sensor from Sony, which is actually a good news (based on online reviews of the A900).
This is a rumor which I cannot confirm.