[...] it would just need to import the map, the vbl and the properties ofthe light sources - so that the light sources work.
And do you see the imported light sources just be added onto the end of the existing campaign properties 'Light' tab? For someone trying to use your maps directly, that probably seems like a reasonable approach.
More fully featured maps would have to import extra property lists. So if the map pack were to have a Set Dressing property list that had a OverallBaseDC value that sets the DC of all open lock checks, search checks for traps, that sort of thing, that property would be available on import.
Is that the kind of information you were after?
Yep, that's a good start. I'll think about this some more and when I get back from Denver in mid-December we can chat about it some more. If you end up working on a map and think of anything, you can drop it here or send me a PM.