To be honest, I kinda expected them to do that at some point. Removing some mons from each game and doing rotating rosters of some sort.
But I only expected it to happen after we actually hit 1000 pokémon in the national dex. After that I thought they'd do a soft-reset of the franchise like BW, and start limiting the games to never have more than 1000 pokémon. Each new game from then on would just change which ones of the 1000+ total mons would be the selected to be the 1000 present in the game data.
I know it's super autistic, but I legitimately wouldn't be that angry/disappointed if they did the purge after a soft-reset and only after we hit 1000 pokémon instead of just 800-something. It's such a minor difference but it would be more symbolic idk