We won't get rid of natural gas any time soon. Ng pipelines are not in any way similar to H2 pipelines except the word 'pipe'. You can't just put hydrogen in them. You can't even retrofit them. You're looking at laying an entirely new pipeline either way.

Furthermore, most H2 is produced by fossil fuel extraction. We aren't cracking water to get H2, we're pulling it out of the ground. Cracking water is hideously expensive.

All in all, combustion engines are more efficient than green hydrogen. That's the core problem. We simply don't have the absurd amounts of unused energy required for green H2 production. If we did, we'd be pumping fully half of that energy into the atmosphere as waste heat.

Hydrogen cars aren't going to happen. We won't have grid-scale hydrogen. It's just a terrible idea. Hydrogen is too difficult to handle and incredibly dangerous to store. The efficiency is so ludicrously bad that you would genuinely do better to create syngas from captured atmospheric carbon and burn it in regular combustion vehicles.

Avoiding carbon emissions is not the only concern in regards to the climate. Focusing on carbon and nothing else leads you to really dumb and bad ideas like piping hydrogen gas across the continent.

This is not quite true. The original gas pipes in most cities were built for "town gas" which was produced from coal and is 50% hydrogen by volume. The infrastructure could handle hydrogen just fine, but the low conversion efficiencies make it impractical.

h2 can be co-mingled with Ng and extracted with a molar filter at the other end.

Ng pipelines are everywhere, so it makes perfect sense.