FIRE folk (and every retiree) are going to get killed by inflation over the next ~5 years. The thing about retirement is that you're on a fixed income, and if you're doing it right you move capital from risk assets like stocks into more deterministic investments like bonds as you get close to needing them. The value of bonds and cash is about to get crushed; it's very hard to plan how much you need to live on when living costs may go up 5-10x or more in the next 5 years.

I really doubt FIRE is popular enough for them to matter in practice. I suspect very few can stand pinching pennies for the 10-25 years it takes to save up the capital.

It probably matters more for highly paid professionals who can do it in 5-10 years.