My understanding on this was that it's more about durability so your terminal hair length is when on average your hair will fall., not their maximum growth because the hair follicle know when to stop.. as far as i'm aware it's not an intelligent feature, just look like it

It's niche because not all pipeline are able to accommodate hydrogen in large quantity, because not all boiler can accommodate high percentage of hydrogen, because not all green energy powerplant is near enough a pipeline to link to it with their hydrogen production, so it's niche because logistical it's a nightmare not because it's not technically doable

Except it's not really, I was part of analysis on the subject and with current technology, even with free electricity (as this would be a mean to offset green energy uncontrolled output) there's no payback to pay for the machine before 10 years unless hydrogen is subsidized

And even then as you said you need a natural gas pipeline near that can accommodate high hydrogen % and natural gas heater in home that can as well which is a logistics nightmare

There's some very niche usage and the one you mention is one but it's far from a widespread technology we can use everywhere

Hydrogen is a dumb idea except for niche usage because of power density vs chemical options

It will never be a large scale solution for anything

Yes even if the byproduct is water

Honestly, we might be at a point short term (under 1000 years old) trade off from biological problems are necessary to offset the millions years old problem that is climate warming through fossil fuel consumption