i think exporting needs to be written by the application - exporting objects generically won't do it all since all objects seem to have different attributes that are important to them and that is package dependent.
Overall though, this isn't hard to do, csv import and exports are pretty easy to set up... (you could take a look at hte CSV import of users in dotlrn, and the csv export of survey answers in the survey package) you just need to want to do write it, and at least for me a regular database dump and restore (or possibly dump and then a cut of the table i want to import to a new db), is much easier then writing this importing exporting feature to do that through a web interface... i only really do this to test something on a development server anyways...
