Yes, the whole "attitude" of GF towards the Emerald elements in ORAS seems to be a nod to Emerald and a hint that the events will indeed occur. For the Entry Call function, I see no issue. It's in development, and will be available when/if finished. But specifically for the Battle Frontier, I could see this being the in- game reason/excuse why the BF wasn't in ORAS. It never was completed after the events of ORAS. Sure, Scott is scouting people, and Pike Queen has been scouted already. But the whole thing hasn't been built, and is eventually cancelled because it bothered the Smeargles in Artisan Cave. Sure, it's a floppy reason, but just like their excuse Takao Unno gave for why the E4 members were not participating in the PWT: they have to guard their regions while the champ and gym leaders are away.