I do want an ability to spend from a lightning wallet at any of the many different kinds of payment terminals in the US

What if you could get it all cheaper, privately, over the internet, paid with sats, without having to go visit brick & mortar? Would that be an acceptable alternative?

I want an easy way to allow people holding fiat

That's not for you, and fiat != bitcoin. The stablecoin mindset is a shitcoiner mindset, because the fiat it tokenizes is a shitcoin AND the tokenization contract doesn't have enforcement to the peg, so that is a shitcoin too. shitsquaredcoin.