In Pokémon Ultra Sun/Ultra Moon, it would be nice for there to be a National Pokédex, although admittedly, it makes much more sense for Pokémon Bank to have it... But it does seem odd to have a Pokémon appear in game without a Pokédex entry.. Funnily enough, when I used an Action Replay on Pokémon Sapphire way back in the day prior to the announcement about Pokémon FireRed/LeafGreen, I forced wild Pokémon encounters to be things like Mew, Celebi, and Articuno (since those are unavailable in Pokémon Sapphire). If I recall correctly, when I caught them, they didn't trigger Pokédex entries and didn't show the National Pokédex numbers on their Summary Screens (although I think things like Articuno do show the number if you migrate them properly from Pokémon FireRed/LeafGreen, and they have viewable Pokédex entries, too). Ah, I remember the first time I unlocked the National Pokédex in Pokémon Sapphire (as far as I can tell, it's triggered by trading a non-Hoenn Pokédex Pokémon from Pokémon FireRed/LeafGreen); it blew my mind.. I think I thought that Pokémon FireRed/LeafGreen magically updated my game with the National Pokédex Mode (as opposed to the National Pokédex already being coded into the game during production before the release to retail).
I guess it would depend on how long it takes to code things like the National Pokédex in Generation 7. Ideally, there would be a National Dex in-game and via Pokémon Bank.. However, it may get tiresome seeing the same old Pokédex entries (soon to be 802+) continue to get ported in future generations (and now even Alolan forms/regional-variants, some other forms, and Mega Evolutions are getting Pokédex entries!), so I can see why Game Freak would relent their efforts.. But yeah, an in-game National Dex would be nice (with Shiny Charm and a 2nd Diploma as the prizes), with regional Dex completion awarding something else and the 1st Diploma.