Thanks a lot for the message.
This is clearly something that we are interested in, and for which we would like to provide built-in support.
However at the moment built-in support is only in the long-term roadmap (maybe late 2018?). A community-driven project based on the CS/JS Interop
may be a better approach.
In any case, please be sure to vote for this feature on UserVoice, where I have just created a new entry for it:https://cshtml5.uservoice.com/forums/274799-c-xaml-for-html5-feature-requests/suggestions/32147959-progressive-web-apps-pwa