Well, I'm happy to report quite some progress. I started a series on NetBeans Zone a few days ago that you should definitely read closely if you're interested in a typical business case involving JPA on the backend with NetBeans view components on top (which is the main usecase described in the issue above):
However, note that I've ended up abandoning Beans Binding completely. Not sure if I'll have time to post the next installment of the series today, because I suddenly made a lot of progress that took up all my time. Below you see the current status (icons stolen from Tom's ToDoLIstManager, but everything else is mine), with, interestingly, the editor component (currently view mode only) and the tree structure being in two separate modules (anything else would have not been a correct NetBeans Platform idiom):
Despite being in separate modules (enabling either one to be removed and replaced by an alternative module that fits into the flow), the two components are perfectly synchronized. The separation between editor and view is done exactly as described in Tim's tutorial. Several issues need to be looked at very closely still, especially in relation to optimizing the JPA and EntityManager parts. However, a lot of the coding is done, at least for the view side of things. Next, I will need to look at how to store the data back to the database via JPA. (Any tips on this would be welcome.) I imagine "SaveCookie" is going to be playing a big role here, which I will need to hook up to the EntityManager. I'll be looking at Tom's "SaveCookie" for sure, though he doesn't use a database.
Once the whole scenario is complete, and I have completed my series on NetBeans Zone, I will turn the whole scenario into a tutorial on the NetBeans Platform Tutorials page. After that, it would be cool to create a code generator that will generate the whole application from a given database, exactly as is done for JSR-296 in NetBeans IDE.