why would they? sprites are dated and no game, let alone pokemon, should be using them anymore. they are implemented by lazy developers who do not want to take the time or manpower to actually program character models and overworlds.
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A return to sprites would certainly feel like a bit of a step backwards. They already started making 3D models, they don't seem half bad to me, and they certainly wouldn't want to have made all of that work and then throw it out the window with the next installments.
I wouldn't care at all. But if the graphics transition is their chief excuse for how ****ty this gen is otherwise, then it would piss me off because they'd basically have made this generation suck for no reason.