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Lots of people are talking about what's happening in Sword/Shield, and not really focusing on the entire thing that Masuda said.
He's not just saying they're cutting out certain Pokemon from SS, he's saying this is an entire policy shift for Gamefreak.
>その結果、今作から対応方針を変えることにしました
>Because of this, from this game forward, our policy will change.
>冒険の舞台に合わせて、拘って登場するポケモンを決めている
>The Pokemon that will appear will be specially selected to fit the stage of adventure
tl;dr Don't ever expect to see every Pokemon in one game ever again, even if they release a Gen 4 remake, it'll still have different Pokemon available compared to SS, and the pool won't be compatible.