Maintenance mode doesn't mean "this is so mature we don't have anything else to add", it means "we don't want to spend any more time on it so we'll only fix bugs and that's it".
Some notable companies using Replicache are Vercel and Productlane. It's a very mature product.
The Rocicorp team have decided to focus on a different product, Zero, which is far less "offline-first" in that it does not sync all data, but rather syncs data based on queries. This works well for applications that have unbounded amounts of data (ie something like Instagram), but is _not_ what we want or need at Marco.