While I appreciate the sentiment and the exploration of this — especially as a type of one-pager landing page for serving up address/phone number type information, overall I don’t get it. Offline web sites? In this day and age of LTE and open Wi-Fi hotspots, this seems like over-engineering for a scenario unlikely to be accessed very often.
This is one of those cases where someone will get a lot of mileage out of this, but most sites won’t get much utility out of this — especially those content-heavy sites.
Again, I appreciate the sentiment and exploration, but don’t think I’ll be spending much time ensuring our fleet of web sites are Offline First. Plus, if you’re offline and need something, I don’t think any site we’ve developed, maintained, etc. are going to be your first (or even second or third) target.