The same pipes that now carry Natural gas around cities used to carry Town/Coal gas in the past and it is about 50% H2 and it worked without any issues.
You can switch to pure H2 distribution without major issues
There is no reason to not do so. It worked fine hundred years back.
It makes sense they want it. With Abundant renewables, there will be windows with electricity at zero or "negative" price. And they can with reasonably big storage make a fortune on using it and storing hydrogen.
It is pretty safe to store it and when it leaks it just safely rises to the sky.
The other thing to realise is that most of the old pipes under roads etc made of iron which are vulnerable to embrittlement, are reaching end of life anyway due to corrosion and temperature cycles. And so they are due for replacement in the next 10 years anyway.
When I lived in Leeds the gas authority there was conducting an extensive replacement process. All pipes were being replaced with plastic or polymer which can support H2. They are currently only carrying CH4, but there is clearly the aim in the future to carry H2.
Also, almost every boiler made in the last 10yrs is capable of burning a part H2 mix without modification. And with some simple modifications it should be possible to get up to 90-100%.
Long term I think heat pumps make the most sense for new homes, and for old homes on a case-by-case basis perhaps. But H2 as a heating gas also makes a huge amount of sense. It combusts cleanly producing only water vapour, has similar energy density to CH4 (a little less but not drastically so) and can use as much existing infrastructure as possible. It may even be possible to fractionate the gas at local distribution, so you can switch an area to 100% H2 once all the boilers in that area have been tested/upgraded.
IMO even bigger than climate change is energy security, if a country can produce its own gas, no more Russia/Saudi/etc. controlling the gas market.