The maximum size will increase to at least 1GB in the near future, enabled by our recent rewrite of the underlying storage layer. Perhaps we can push it further, even, we'll see.

But yes, I think the next step is then some sort of sharding. Sharding by user would be an obvious approach for many apps. I think we should build a framework to help manage this, so apps would only need to provide some callbacks e.g. to compute shard key for a particular query.

Alternatively, apps that want full control will be able to use Durable Objects directly. We'll soon (in a few months, probably?) enable the new storage engine for all Durable Objects which means every object will have a private SQLite database.

(I'm the tech lead for Workers in general, and currently focused on this project in particular.)