Given how NixOS is structured and developed, I am not sure running on unstable is for everyone, maybe stable boot system / DE configuration with high-churn applications (which will not be that stable or that reliable in real world whatever version you use…) installed from unstable, and maybe some high-impact high-quality well-stabilised software installed from unstable.
I usually rebuild my system from master, though. Maybe rolling back if it gets too broken… But I also split the package set into many shards, which can be rolled back or delayed independently.