My parents are using a smaller open frame to run a electric heater, a few lights, their fridge and the well pump during the power outage in Michigan. It's costing them $36 day to keep it going 24/7. A natural gas generator would be wonderful.
OTOH the people in the towns north of here that were hit by the floods earlier this year had the natural gas shut off for weeks and I read read reports from people that couldn't use their stand by generators at all.
I agree that a dual fuel system is best but how do you keep enough fresh gas on hand to run the generator for longer than a short time? Diesel last longer doesn't it? Will it run in the same system as NG? You could also get a pig to hold propane as the back up, it wouldn't last forever but wouldn't go bad either.