A report designer and generator. This is one feature that will really separate FF from the pack.
It could include, in addition to all the usual report design features a data model. You'll need some sort of support for whatever DB's you want to support to base the model on. SQLITE3 could be a good choice. Since, at run time, you wouldn't have a guarantee of where the DB is, the location could be abstrated based on the definition of an alias that would point to the path and file name.
The generation output might able to be piped in PDF layout to some browser window.
Rick Kelly