I have a Nikonos V and still use it occasionally. I've always thought it would be great if Nikon would make a digital version of the Nikonos, but there are problems inherent with making a small non-housed camera.
One of the things that made the Nikonos so small was that it didn't have anything but manual focus. The Nikonos RS came out with auto-focus, but the camera was huge.
I think, today, no one would want a camera that didn't have autofocus. That means that the lenses would have to be encased, "housed" if you will, which would increase the size and cost of the camera. Then there is all the electronics needed for a digital camera. And the large lcd screen that everyone wants. And a needed lock down door for the digital media, another "housed" area of the camera. Pretty soon, you'll come to the conclusion that if you want an underwater camera with autofocus, digital media and a lcd screen on the back, the most economical way to make it is to house the camera. Then, of course, you can sell the camera to people who have no need for the housing in the first place.