Apart from implementing the spec I think we should use the singleton case to blueprint component extensions.
If possible we should 'freeze' our current component set (ejb3-core, metadata, ejb3-api) and create a new component set which expand on the existing ones. This probably means the existing ones need some modification to make them extendible, but those changes must be backwards compatible.
Also the concurrency part I would like to see in a separate component. We may want to add it to other container types as well.