There's at least one customer out there who has an RPi with NixOS on it from me. Probably still works to this day. It was the best use of NixOS I think I've ever found.

I've switched up to NUC-ish hardware which WAS cheap until recently. All the components just a bit higher quality than the lowest-bidder you get on the Pi. Run nixos on that and you've got a really solid platform.