Alas, houses appreciate, cars depreciate, and RVs are just worthless. I exaggerate, but RV depreciation is absolutely nothing like auto depreciation. They lose 25% driving off the lot and another 25% per year (numbers out my ass, but correct order of magnitude).

The cost certainly would the most make sense on gigantic $300k class As, which also conveniently have space for lots of panels and lots of batteries. And indeed you see the most elaborate factory-installed solar setups on those beasts. That's a tiny market, though.

I think you're right about the future. It won't be long before thousands of watts of solar come standard on most RVs. In fact I don't think it will be all that long (decade or two maybe?) before the RV is clad in some kind of solar material. Like every square inch of the surface is generating solar.