As of ~2011, Generac generators were discontinued for RVs.
As far as I know, the only onboard gensets available now are Onans, or for diesel, the 3000 watt PowerTech. Yes, one could spend the ten grand and go for a marine grade 5000 watt Kohler... but if that breaks, you pay marine grade prices to fix it.
I think there is a market niche available. If someone could make a generator that used EFI, an inverter (so the genset could run at an idle), and perhaps a small battery to absorb load until the engine got up to speed, they would make a mint. Even a generator going with four poles instead of two would be nice (1800 RPM instead of 3600), or using oil pressure instead of splash lubricating.