I have thought the same thing! I spoke with iNat staff about this issue, and they said that the way the CV is currently set up, it can’t consider groups that are nested within each other. Furthermore, adding all these extra groups (whether you do branches or pseudo-leaves) will dramatically increase the complexity of the model and lengthen the training time. What levels would you include: genera, families, classes, orders? Subfamilies, tribes, subtribes, subgenera? I think ideally you would include as many branch taxa as you could, but just duplicating all eligible genera (that is, using at least one leaf for the species in the genus and then a second pseudo-leaf for the remaining observations) would be a lot! I can appreciate that concern, since the training set is already growing very quickly on its own.