As a user I always wished Firefox OS had stuck around - I think it would absolutely be practical today with so many PWAs around these days, and KaiOS seems to have done surprisingly well on its Firefox OS base.
But that's the thing, KaiOS is exactly the best that Firefox OS could have hoped to achieve: installs on most feature phones. Sure, it's hard to find a phone with KaiOS in the West, but Firefox OS could have never hoped to be an alternative to Android.
Is KaiOS still being used in any newer feature phones? I believe even its biggest customer Jio Telecom has moved on to android in its entry level phones and any new feature phone I see here (India) occasionally are Nokia.
There are still some things I like better about FFOS than iOS / Android. It had a lot of polish needed even near the end, but some of the foundational bits were very solid.
