Agree with dom96. PWA has very vague definition, even in JS-land it's not clear of what exactly are PWA or PWA-framework.
Just using JS API from Nim should be enough. P.S. I would stay away from PWS, both Apple and Google are against it and making it very complicated to provide native-like experience in web (even if they publicly say they support it) as they want you to use AppStore and pay money and all the purchases go through them.
