The main reason why research on this topic is sparse, and why it may be difficult to enlarge Krippendorff's coefficients to overlapping units, probably results from the fact that we are facing here a major difficulty: the simultaneous double discrepancy between annotators, with annotations possibly differing both in positioning relevant units anywhere on a continuum, and in categorizing each of these free units.
it is difficult for a method to choose precisely which features to compare between different annotators (unlike pure categorizing, where we know exactly what each annotator says for each predefined element to be categorized); and this problem is exacerbated when overlapping units (within an annotator) occur.