One of the reasons a 603mm diameter rim might be useful is that it would allow a wider tire and a fender to be used on many existing frames. Some of us have come to appreciate the comfort of wider tires and fenders. It might not be a wacky idea at all, but since the rim and tire combination doesn't exist we won't know.
The reason the project never materialized was that they couldn't find a tire manufacturer to make the tire.
There was a recent Bicycle Quarterly test comparing the performance of various wheels of different rim diameter and tires of various widths. Their conclusion was that smaller diameter wheels are less stable than large diameter wheels. Wider diameter tires help make smaller diameter wheels more stable, but make larger diameter wheels too stable. There is an interesting discussion of the various forces involved in the bicycle wheel. I'm not sure that their tests are perfect, but at least they have tried to make real world tests of various rims and tires.
The test was in the Spring 2010 issue, vol.8 no.3. I guess you have to go to the paper copy as they don't make their issues available on the net.