Wait so if there is no national dex then there's likely no more Pokemon catching in the post game, specially since it looks like the only possible post game area is the big city up north.
Also since there is no national dex and no megas its likely there will be battle facility this time around: battle tower clones always used all pokemon, thats one of the things that made them challenging. I cant imagine a battle facilty that only works with regional dex.
Obviously there's no chance for Frontier or PWT because, again, no other Pokemon
Obviosuly Kalos wont be in (not that it was likely in the first place) but since megas are gone and Kalos is about megas. Unless it would be Kalos "A world where maybe the evolution of Pokémon took a slightly different path, where Mega Evolution is unknown..." as Zinnia said but such alternate reality that would be way too ambitious for GF

So...what will be as post game? Legendary Pokemon and some short extra story? Welcome to 2019 when Pokemon shrinks on a more powerful console. Hey but we get BOTW illusion with Wild Area. Thats cool...right?