Actually the Olympus manager stated that they intend to stick to 12MP for the 4/3 sensors, and improve other aspects of imaging.
http://news.cnet.com/8301-13580_3-10189546-39.html
Actually, no such definitive claim of "never more than 12MP" is made, despite that being the way that many people read his statement. My reading is that Olympus feels that
1. resolution increases are now a lower priority than improving other aspects of IQ, so big or rapid increases in pixel count beyond 12MP should not be expected
2. 20MP is the limit for the foreseeable future for all formats smaller than 35mm full frame.
I would go only so far as to predict that the next few 4/3 models with offer "12MP" sensors with the current pixel spacing, but improvements in other respects. Panasonic already claims as much for the new GH-1 sensor, and the 10MP sensors went through several such incremental improvements. I severely doubt that the 4/3 partners will stick stubbornly at 12MP if APS-C DSLR's get to the point of having smaller photosites than 4/3, meaning going beyond 20MP. Panasonic uses the same MOS sensor technology in phone sensors of far smaller pixel size, so the technology is not close to its minimum possible size.
Below are some quotes, with emphasis added. (Aside: Olympus has now officially accepted the neologism of using "full frame" as a synonym for 24x36mm format!)
The first comment sounds a lot like something that Michael R. said in a recent essay ... but his new camera has a bit more than 12MP!
"Twelve megapixels is, I think, enough for covering
most applications
most customers need," said Akira Watanabe, manager of Olympus Imaging's SLR planning department ...
"We have no intention to compete in the megapixel wars for E-System,"
Instead, Olympus will focus on other characteristics such as dynamic range, color reproduction, and a better ISO range for low-light shooting.
"We don't think
20 megapixels is necessary for everybody. If a customer wants
more than 20 megapixels, he should go to the full-frame models"