I know Sync is brand new, but I think the Custom Apps API should add the following properties:
isSynced: boolean, similar to a field’s
sourceTableId: similar to a MultipleRecordLinks field’s
sourceViewIdfor the source view
sourceBaseIdfor the source base
sourceRecordId: similar to a MultipleRecordLinks field’s
linkedTableIdproperty, but reporting the record not the table
Hopefully these won’t be too difficult to implement because boy would they be life savers!