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Using Metroid as an argument is dumb as hell. The Prime games weren't successful because they "changed the formula," they were successful because they were good games.
Super Metroid is still considered one of the best games ever made and was only the third game in the Metroid franchise, there was nothing stagnant about it. Its proper follow-up, Metroid Fusion, is also considered a good game but is mostly criticized for being too linear, departing from one of the core appeals of the first three games which were well known for allowing the player to "sequence break." Metroid 1 and 2's remakes were plenty well-received and they largely stayed faithful to the originals' gameplay.
The Prime games are all highly praised because they were solid FPSs in their own right, not because they "fixed" a franchise that needed to adapt or were "improvements" over the older games. Prime 1 and 2 both came out alongside successful 2D Metroids that stayed true to the original style of gameplay.
I don't think it would be bad at all for Pokémon to experiment with the IP in varying gameplay styles, but I don't think the core gameplay of the series is fundamentally broken.
I haven't finished a game since XY, but the gameplay was the least of my problems with ORAS and SM. My biggest problem with SM was not being allowed to play the game enough.
I would welcome the Pokémon IP being opened up and being explored to its full potential and the biggest reason would be getting more Pokémon games that weren't held back by Game Freak's lazy-at-best development.