By the looks of the images they released, spawn eggs will only be stackable to 16. This is a big negative for mob arenas for it will limit the amount of eggs in a dispenser I'm not positive that they only stack in 16's but in every image they are only in groups of 16. I really hope they change this before the update... :/
I think you'll find he probably got them out of a dispenser, where '16' is the max. I kinda doubt that eggs would have a limit of 16, this would be 'quite' different then the PC version, but I could be wrong. I can't remember if the PC version ever had a limit of 16 or not but i don't think so.Even PC dispensers stack at 16, with 6 slots.
Stay fluffy~
Unless making a mob arena with multiple levels which would need more eggs.
I'm not familiar with mob arena's but if 144 enemies aren't enough why not just use a second dispenser?
Adding to that...wouldn't an array of Dispensers would better than one set to a loop?
Or are you going for a "One at a time" theme?
Stay fluffy~