The Minchas Chinuch makes a brief observation that one cannot be in violation of an issur chameitz (on a d’oarysa level) by owning wheat which is kilayim. Since kilayim must be burned, “kitusei michtases shiurah”, i.e. anything halachically must be burned is assumed to be non-existent and less than a shiur, so one does not really posses a shiur of chameitz.
I was wondering about this. All the cases I recall of “kitusei michtas shiurah” apply the principle l’chumra, e.g. if you have a lulav which is made from an asheira tree, it is disqualified because of kitusei michtas shiurah. Here, the principle works l’kula. Is it such a davar pashut that the principle can work l’kula as well? Are there any similar cases you can think of?