To restore backing store capabilities since we migrated to interfaces we probably need the do the following:

in abstractions implement IBackedModel with a proxy. That proxy would take an IBackingStore as a constructor parameter and route calls to the backing store accordingly.
there might not actually be any changes needed to the generation work at this point (or we should remove the backing store assignment from the model constructore/factory)
in the serialization library instantiate the implementation from point 1 here when the backing store is in use (we could add a constructor parameter/readonly field in all parseNode implementations, and that field would be set by the respective factory. In turns the factory could have a property (getter/setter) in the ParseNodeFactory interface, which in turns would be set by the proxy factory )

TypeScript - Backing store support #2613

Description