Well maybe it's like saying "vanilla furry sex"? you know, being averagely normal sex outside of the interspecies thing? Unless yukkuri count as bestiality...or whatever is called what that guy from American Pie did with the Pie itself...
Well, furry is borderline bestiality or worse. When it is humansex, the yukkuri at least have some kind of body closely resembling a human female, but the head is obviously yukkuri.
Like one of those Aya types with ultra hot bodies in hot human-yukkuri action. Were it not for the head, nobody would care. Wasn't there an artist who did a comic ("Bride Reimu", I think) who made a comic on exactly this idea?