The frame reminds me a bit of a Mountain Cycles San Andreas; two halves shaped and formed then welded together. But I don't see anything that makes the ebay prototype really desirable, except to a Verlicchi or Ducati collector.
Most desirable retro bikes were early models from builders/companies that went on to success later. Team replicas or actual bikes that were ridden by successful racers also appeal to some. The same with an innovative bike that introduced a new design or feature, but may not have been successful as either the technology or the market wasn't quite ready at the time. And still other old bikes were ones that we lusted after, but we didn't buy or couldn't afford.
I don't see the one on ebay checking any of those boxes. Rare does not necessarily equal desirable.