Depends on how decentralized you can inject hydrogen from overflowing renewables, then. If you could do so at the city's connections to the main long-distance network, it might not be economical to have the infrastructure to create methane from it, and, on top, the hydrogen fraction would be CO2-free even if burnt in a normal boiler/stove. I wonder what upgrades would be needed, though? Are they not already using one of the steel alloys that is resistant to hydrogen embrittlement?