You are right, most businesses that run that type of logic probably have the money to afford configuring master-slave based systems. They probably should not move over to GUN.
No, you do not have to use S3 for persistence, you can also use your disk. Persistence is a plugin in GUN, so you could build your own module that uses anything to store data.
However, there are lots of interesting advantages to distributed/decentralized master-master systems. And I'm trying to make those algorithms available to common man.
Thanks for the encouragement, I'll be adding more docs and blogs and stuff.
Edit: This person (in the comments below, please upvote him), and my reply, best addresses the most important questions: https://news.ycombinator.com/item?id=9077969
Persistence is solved with "any S3 like service"? So what does that mean, using Gun is going to tie me to another unrelated Database as a Service that I'm going to have to pay Amazon for?
I'm sure this tool offers something interesting that other tools can't match, since you made it and put time into it, but the existing documentation isn't capturing that yet. Write up another blog post that describes the details, the use cases, the guarantees, etc.; i.e. the actual hard technical details, rather than the PR-speak, and I'll happily take a second look.