Resource lists:
Tools List:
https://www.pwastats.com/
https://pwa.rocks/ 
https://codelabs.developers.google.com/pwa-roadshow 
https://github.com/zeit/next.js/issues/861
http://offlinestat.es/ 
https://pouchdb.com/ 
https://docs.datproject.org/ 
https://developer.ibm.com/clouddataservices/offline-first/ 
Further reading:
TwinPrime Mobile Usage Stats: http://twinprime.com/lte-has-slowed-by-50-in-the-us/ 
Lara Hogan, Etsy, “Designing for Performance” http://larahogan.me/design/
Nolan Lawson, Microsoft Edge,  “Progressive Enhancement isn’t dead but it smells funny” https://nolanlawson.com/2016/10/13/progressive-enhancement-isnt-dead-but-it-smells-funny/ 
Prosper Otemuyiwa, Google,  “Introduction to Progressive Web Apps (Offline First) - Part 1” https://auth0.com/blog/introduction-to-progressive-apps-part-one/ 
Pedro Teixeira, YLD,  “Building realtime collaborative offline-first apps with React, Redux, PouchDB and WebSockets” https://blog.yld.io/2015/11/30/building-realtime-collaborative-offline-first-apps-with-react-redux-pouchdb-and-web-sockets/#.WPe4Tj9926k 
Jesse Beach, Facebook, on Conceptualizing and Expressing Offline to the End User https://medium.com/@jessebeach/my-biggest-takeaway-from-the-second-offline-camp-in-santa-margarita-ca-d0dd930cd02b#.epml3r1tx