Our Hot water systems are already on a simillar system (It only runs at certain times of the day and is a different tarriff).
But even with that, your talking about adding a huge load, which where I live in Summer, people run their aircons all the time, (morning and night), so it still wouldn't be feasible without some huge upgrades to the transmission and generating capabilities.
Not to sure about the hydrogen over your natural gas lines either. Not a piping engineer but I don't think they run at the same temp when compressed. Maybe I'm wrong. So you would be looking at different pipe, flanges, gaskets the whole deal.
But hey, glad to see your thinking about it. and I love your motive, (Make Fuel cheaper for us, hell my car was drinking 20ltrs/100km, so I need all the help I can get).