I gave this some thought below, but unfortunately fitting a new, more expensive sensor is probably not going to happen soon. The current 1.8 megapixel is a cheap commodity sensor, and it's still probably costing them buckets to have them fabbed with their custom microlenses. Something like a Kodak 8MP sensor would probably be 20x as expensive, and talking them into making you a custom SKU would be much harder.
Edit: after a bit of digging, it looks like they make the micro lens array themselves and buy the sensors without one. This obviously makes acquisition easier, but as the pixel pitch decreases ( by an order of magnitude, to compete with a modern SLR ) the complexities of building and attaching that array increase significantly.