AFAICT this should be possible already using user defined XML extensions, that said I've never really tried to do this myself so I cannot really say how easy or straightforward this is.
On the other hand if what you really want is a package filter to show only packages of interest, there is the filter option in the right click menu of the packages node that does just that, it's only limitation is that you cannot maintain multiple active filters, so if you want to have all packages starting with BR and all packages starting with IT in 2 different nodes you cant; but you can definitely define an OR filter and have these packages only in the default packages node.
Yes, you can do this. It's possible via a XML extension. You need to supply a bit of SQL and XML code. The XML specs are here
See the 'folderType' section.
Also, probably you are aware of, in the Connections view and the Schema Browser, the ability to filter on ...
1. Object names in a schema
2. Object names of a specific object type
These filters persist between sessions, but for each schema, and each owner+object type combination, only one filter expression (with multiple conditions, either all using AND or all using OR) can exist.
Possibly closer to what you want is the much enhanced Find DB Object feature in 4.0. It is quite powerful, the search result tab can be pinned for the duration of the session, and clicking on an object in the results will open a browser/editor on the object (which can also be pinned). These search result cannot be given names and persisted between sessions, but try it, you might like it.
SQL Developer Team