Do you have a CI/CD pipeline targeting all the systems with a base config and target-specific  host configs? That sounds like the dream. 

I wish there was more thoughtful integration of git into the nixos-rebuild workflow; like, to achieve commits in lockstep with NixOS generations and some sort of association between the commit and the generation hashes? I guess people might do this with hooks? 

 Not CI/CD but a cron job that runs a script that git pulls my nixos config from my git server and does a nixos-rebuild switch.

Then I also have syncthing syncing my home dir for all app configs/states across machines. It feels damn close to using the same computer when I switch from my laptop to my desktop. 

 Though I do have a base config and then specific host configs that automatically switch based on the hostname.