What if we aren't getting any new Arcade updates because it would mean having to make Shadow Lair counterparts for the bosses and stages for high tier players? You know apart from having to actually getting the workforce to make something entirely new.
Can't think of anything more, but just tossing a theory into the air.
Well, if there was to be a new boss, it would most likely be done in stages. Boss strata gets released first in the arcade and/or in the missions first then they can add them bit by bit. Missions, for example, were released in two stages. When first released, it went as far as the Roarmulous Twins, the rest came after.