I suppose "local-first development" is a misnomer. It's really about the syncing part. Currently we have traditional applications that write data locally and therefore don't require an internet connection to work, and we have online stuff that updates a shared state "live". The "revolutionary" part would be having both of those things. It's a surprisingly hard thing to do.

The current state of the art here is git. So we're basically talking about making git automatic and easy to use for the majority of the population. That's not something we've been "doing for decades".