Could an oil pressure light, rather than the FJR's oil level light, perhaps have saved this, or at least limited damage to repairable bearings/journals? I suppose that depends upon where oil pressure is measured. As I think about it, probably not.
I think part of the problem with an oil pressure light/gauge would be convincing the potential owner(s) that having less than 5 psi of oil pressure warmed up at idle is normal. It's in the service manual, check it out.
Were the bad rod journals the farthest from the oil supply passage inlet? May just be that do to excessive oil clearance in the others that no oil was left to get that far. Then again, if it was that bad I would think it would have had rods knocking before going.
Here's what (half of) my crankcase looked like when I split it open:
The gallery that feeds the main bearing journals is directly beneath the main bearings, and oil is delivered from the main bearings to the rod bearing journals through passages drilled in the crankshaft. The damaged journals on dunhamg's bike were the rod journals of cylinders 3 & 4, which would be on the right side in this photo. What feeds the main bearing gallery is the gallery that runs perpendicular to it. That's where the pump pushes oil through the filter and oil cooler before feeding the mains.