Fascinating question! It's something I've been thinking about for a while. Now that we've got Streams and Service Workers in the platform, there are opportunities for super-high-performance content site, but they require some collaboration between the templates the server uses and what the client understands.
I've been impressed with Surma's work on WordPress PWA templates
The thing that seems to be missing from most content-oriented PWAs is a way to sync sections for offline reading, so starting from something static-site oriented might be my approach.