These days there are several 1K+ HP engines to choose from, but they are relatively recent developments. Back then, the auto industry was still stuck in what we now call the "Malaise Era," and high-output motors were not exactly thick on the ground. Taking two of the best of what was available probably seemed like a reasonable approach, but the operational and logistical complications probably doomed the program. Also, the tiny unflapped high aspect wing was the most efficient way to carry the thing, but it necessitated high landing speeds and left little margin for error.Bob Pond spent millions trying to do a scratch built Unlimited. Best speed they could ever get was 400 mph. It would have taken tens of millions of dollars more to ever make it competitive for the Gold, if ever.
This year, the faster Sport airplanes this year were nipping at 400 MPH, and none of them were multi-million dollar airplanes.
I agree that the Unlimited class should call for a minimum weight, but I also think it should be a good deal less than it is now. It should reward crashworthiness without penalizing innovation.