I feel as if the Battle Frontier is really engaging and that's extremely hard to find post-game anyway. It really should make its way to being a core feature. It also gives us something to breed Pokemon for aside from competitive. Overall it's a very nice feature and it makes us want to put more hours into the game to complete it. I think the Battle Frontier is the main reason why Emerald is such a loved game in the series. I haven't finished Moon yet, I hope to find the time to finish it this weekend!