I wrote a clunky import package for birdnotes.net that is now in ACS 3.5 (kept by Sussedorf and Roy). A service contract-based package to do something similar would be really nice, I think.
Basically the one I wrote that's in ACS 3.5 lets you define the routines to import the data, list the data, delete the data etc. Then there's a manager that just interfaces to these routines that are defined for import type. It knows how to show you error logs generated during import, view the data and a bunch of stuff like that.
In other words it has a plug-in architecture but built manually rather than using a nice plug-in facility like service contracts (because ACS 3.x doesn't have a nice plug-in facility).
I think the basic approach to managing imports is pretty good. On birdnotes I have import plugins for a variety of things we've needed to upload in bulk, mostly sighting data in various custom formats. For SloanSpace V1 I wrote import code for bulk-uploading users.
Export would be easy.
If I had time I'd sit down and write a 4.x version myself!
