gecko

You could ask on the NixOS Discourse? I'm sure people would be happy to share some fun stuff. I would, but I haven't fully removed all the secrets from my config yet :D

https://mobile.nixos.org

I know nothing about this project, but some effort has seemingly been put into this idea already :)

Personally, the more devices I can use NixOS on, the happier I am.

No, not by default. There's other people's work that lets you do this, but you're likely best off doing it yourself by generating qemu config files and systemd services for them through Nix.