Could we possibly change the way in which the instantiator instance is handed over to the Ejb3Deployer? That is, moving from creating the instantiator in the appropriate deployer and adding it as an attachment, to registering a BeanMetaData item and letting the MC do the wiring. The latter could be helpful, since for example in the case of Weld integration we need a reference to the BootstrapBean and letting the MC do the wiring would ensure both the dependency injection and proper ordering of components (e.g. EJBs including singletons are not started until the instantiator is ready).
If the instantiator mechanism is to become more generic and used in other cases, then using the MC would help.