I don't think a Pokémon game would be cross-gen either way, but Legends Z-A is the only opportunity they could get, since it's a game that won't be releasing in two different SKUs, thus, they wouldn't be having the hassle of putting out 4 SKUs on retail for two different consoles.
But as Neoxon said, TPC doesn't care, it's not their responsibility to sell hardware. they want the bigger userbase, and it's on Switch, and they won't gamble on Switch 2 at the start.
and since the game will simply be playable through backwards compatibility on Switch 2, with or without enhancements and performance boost, Nintendo can pull that old trick for the package and put a simple sticker on it lol
They also apparently intended to do the same with late GameCube games and reprints, but never commited