One disadvantage of an electric only supply system, so far as it can be done at all, is that it entails simply scrapping the existing NG supply system and writing it off.

That is a darn expensive way of doing things, so perhaps talk of the cost of upgrading NG supply to use hydrogen needs to be put in the context of the alternative total write off.

Dismissals of using hydrogen in the home also rely on its supposed inefficiencies, based on the most inefficient possible way of doing it, replacing combustion natural gas with combusting hydrogen.

Incidentally, there is little or no doubt that that solution is technically possible:

https://www.hydrogeninsight.com/innovation/government-funded-hydrogen-heating-pilot-in-german-homes-deemed-complete-success/2-1-1645584

' A government-funded hydrogen heating pilot project in German homes has been deemed a ‘complete success’ after making it through winter without any problems.'

But there are better ways of doing things which are way more efficient.

That is through a combination of heat pumps, fuel cells, and perhaps this new tech for heating using hydrogen without combustion:

https://www.azocleantech.com/news.aspx?newsID=34874

' Newly formed technology company HYTING has developed a safe, highly efficient, carbon-free forced-air heating system (patents-pending) that uses a unique catalytic process to turn hydrogen and oxygen from air into heat. Unlike systems that rely on hydrogen combustion to generate heat, HYTING’s technology does not produce any CO2, NOx, or particulate emissions – the only by-product is water.

The process is also inherently safe, as it does not use flammable concentrations of hydrogen at any operating point. The hydrogen is supplied at the same low pressures typical of natural gas supplies – around 1.5bar – so costly and energy-intensive compression and storage is not used. And unlike other technologies which rely on hydrogen, such as fuel cells, HYTING’s heating system works on commonly available hydrogen sources: high-purity grades are not necessary.'

Note that the article's critique there that fuel cells require very pure hydrogen only applies to some types of them, although SOFC and HTPEM are at an earlier stage of development.

And:
' HYTING’s technology can work alongside heat pumps to form a hybrid and completely CO2-free heating system that can overcome these shortcomings and ensure effective heating under all conditions. This also optimises installation and running costs because the heat pump can be sized at the power rating where it is most energy-efficient, with the HYTING technology supplementing total heating output on cold days and taking care of peak loads. The scalability and flexibility engineered into the technology from day one also means that it can function as a back-up heating source, if needed, or as a standalone system.'