Ideally I think Nintendo may want to try and aim for one big title every 6 months at minimum. Is it hard? Sure, but no one said this was supposed to be easy.
1H 2019: Animal Crossing Switch (+ Fire Emblem)
2H 2019: Pokemon Gen 8 (+ Mario Maker Switch)
1H 2020: Mario Odyssey 2 + Switch Pro Model (+ Metroid Prime 4)
2H 2020: Zelda: BOTW2 (+ Luigi's Mansion 3)
1H 2021: Donkey Kong Country 3D platformer (+ Paper Mario Switch)
2H 2021: 2D Super Mario Bros. (+ Xenoblade Next)
Then ideally you would also have one smaller scale seller, but something still significant per half too, like Fire Emblem to go with Animal Crossing, Mario Maker with Pokemon Gen 8, Luigi's Mansion 3 to go with Zelda: BOTW2, etc. etc. Of course you have more games overall, but getting a 1/2 punch every 6 months is a decent way to ensure that you're not losing too much momentum.