IMO the nix language is excellent as templating language, I'd happily use it instead of jinja2 for generating html at a daily job, maybe this will be possible at some point.
The language is alright, the documentation and rate at which things change is the issue.
You wanted to do something and found a page about how to do it? Cool, good chance it won't work anymore cause it changed. If you do get an error from nixos-rebuild because of your nix files, the error report will probably not be useful either.
IMO the nix language is excellent as templating language, I'd happily use it instead of jinja2 for generating html at a daily job, maybe this will be possible at some point.