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Gamefreak never plans on adding the Nat dex back again, this means that every Pokemon game after this is going to have a rotating door if available Pokemon, i.e the Pokemon that aren't in this game will be available for the next game, but the Pokemon that are in this game are more likely to be cut next game.
All your bros are confirmed, but they aren't safe. Come next game they can get cut and will be trapped on a now obsolete SnS unless you want to give GF money for Home where they'll be imprisoned till GF feels like selling them back to you.
As soon as you start thinking longterm you realize how shitty this is for everyone.