I think the article drifts a bit far from "Local-First Software" but I learned a lot about the issues dealing with real time collaboration.
I'm just about ready to release a new version of a web app I first released in 2002 that offers a Local-First option. That's been a goal of mine since I first released it. indexedDB works, but that's a pretty awful option for the app I'm speaking of.
I'm using CouchDB to do this, and it requires the user install CouchDB on their desktop PC. That's a pretty big hurdle, but it's actually very easy to do. I think the hard part will be convincing users it's worth their effort.