I think "offline" is sort of a smell test for decentralized. The problem isn't cell coverage, it's resilience. Centralized networks can implement censorship, get hacked, lose your data, become unavailable, and have to be accessed in a particular way. With scuttlebutt, you none of those particular limitations exist, at least in the same way.

Why does it need to? Isn't that implied by the design? Non-proprietary software that doesn't need the internet to communicate. Where would the censorship fit in?

I imagine that's implied by the decentralisation. How could you possibly implement censorship, given its design?

The canonical app could have filtering built in, then if either you or the other person on the end is using the canonical version, the messages would get filtered. It's very likely everyone would be using an alternate release of the client.

As possibly alluded to by fabianhjr, one of the developers of Secure Scuttlebutt quite literally lives on a boat without internet connection for long periods of time

It is when many users are solarpunks living on boats.

For much of the world, yes.

Yes, not everyone even has cellular data.