Ability to manage extraDbs inside of backend instance

I have one usecase: to manage the set extraDbs in the instance of sharedb/lib/backend

I have successfully expanded this instance with two methods: addExtraDb and getExtraDb.
You can see how I did it here: racer-model-rpc/src/backend

I would like to know your opinion on such extensions for an existing sharedb/lib/backend class.
Are you planning to redesign such overloaded class or create additional management methods for extraDbs? What is the future of such a special option extraDbs?
Please help me clarify the situation!

Although, I understand that we have ability from outside to control extraDbs as an option during initialization or with direct access to an object variable like instance.extraDBs. But, I need to have isolated access to extraDBs to setup an extra DBs in case of the backend instance is already defined.

Start with lib/backend.js, especially the extraDbs handling referenced in the issue, and compare it with the example in racer-model-rpc/src/backend.js. The issue is seeking a design decision about isolated extraDbs management rather than specifying a concrete change; done would require an agreed API and corresponding implementation scope.