There is no OAL required. Look at the Ranch Hand/Mares Leg, or the KSG tactical. Both NR and under 26", because they don't fold, collapse, etc.
Of course if it's too short the Lab might just call it a handgun like they do the 9" barreled Mares Legs...
Also, FNAmerica says this 16" barrel version is just over 26".
Man that could make sence! I am not really a fan of 22, but in that 50 round mag body size you could squeeze how many 22? 65 to 80? That sound interesting!