>>22369323Z will should a postgame for two reasons.
First off, after the backlash from how terrible ORAS's postgame is, they can add the Battle Frontier and say how they "care and listen to our fans". It's a bunch of shit but it drums up good PR for them.
Secondly, they need to give people a reason to buy the game, and I don't think a dozen or so Megas is enough. Only reason ORAS sold was due to nostalgia. Z, if a traditional 3rd game, doesn't have such a gimmick.
But GameFreak is really fucking lazy and this wouldn't be the first sime they skipped something they should do. They know people will buy Z no matter what because they slapped the Pokemon label on the box and consumers are weak.