It's FOSS, with optional free service to host your history (encrypted with local key), I think there's a paid option above a free tier

You can also host your own backend

There's currently no paid option. Obviously one should assume such a free service can't be sustainable so you'd be correct to think we should have one.

Currently we rely on Github sponsors as well as our own additional funding

With the server, is it primarily a gateway to the hosted SQLite databases?

eg receives incoming shell history to store in the backend, and maybe do some searches/retrievals of shell history to pass back? eg for shell completion, etc

If that's the case, then I'm wondering if it could work in with online data stores (eg https://api.dbhub.io <-- my project) that do remote SQLite storage, remote querying, etc.

We currently use postgres. The server is very dumb, verifies user authentication and allows paging through the encrypted entries.

There's a PoC that allows it to work with SQLite too for single user setups - and we are thinking of switching to a distributed object store for our public server since we don't need any relational behaviour.

As a data point, we're using Minio (https://github.com/minio/minio) for the object store on our backend. It's been very reliable, though we're not at a point where we're pushing things very hard. :)