I have a BCS model (Sharepoint 2010) that implement incremental crawl with ChangedIdEnumerator.
My model service implements three methods (ReadItem [SpecificFinder], ReadList[Finder] and ReadChangedList[ChangedIdEnumerator]).
The ReadList[Finder] is marked with the property Rootfinder, in order to the crawl use it in full indexing.
The full crawl works, but the incremental crawl, that should execute the ReadChangedList is not called, instead the the ReadList is called again and a full indexing is performed.
I haven't found a working example for this scenario.