I have no idea whether Robinson are developing a diesel Robbo, but here in Europe where Avgas is both very expensive and soon likely to be scarce it seems like a great idea. Avgas is around 90 p per litre with Jet A1 around 30-35 p. Aside from reduced fuel costs, you don't get carb icing, and I would much rather carry a tank full of Jet A1 than Avgas around with me.
All of these things matter much less across the pond, let alone in California. I hope the rumour is correct or stimulates the factory or some other outfit to look at it.