It’s finally ready for mass adoption, IMO. Also, things take a long time to catch on and now that flakes are fairly stable and a lot of pedagogy is popping up in the form of other people’s configs (and the documentation is being actively improved to hopefully someday meet the high standards of Arch), people feel empowered to try it out.
IOG uses it for their entire stack which is packed with incredibly solid (IMO) software engineering decisions from top to bottom.
I tried it because I wanted to run a Cardano stake pool and develop DApps for the Cardano ecosystem. Their build-from-source instructions made me realize how much better it would be to install it with Nix instead of the cargo cult/curse of the current era, a Docker container.