In our particular case, we have an integration application that allows the synchronization between applications.
We we're trying to avoid the document duplication between the new NAB (NAB2) and the Bildr, for instance. But, in performance terms, having it all in the same application, seems to be better (Bildr doesn't need so much information as the NAB2 have).
This NAB, as an application, it's just a NAB. The complexity is in the documents integration between applications. So, for that, we have an integration application.
I think that a good hint for developers would be create a copy of the NAB and a simple agent that copies information from one application to another.