I feel like this would be reasonable blue print looking long term. You wanna keep strength in those later years and not collapse down into sub-15 mill and sub-10 mill years by year 5/6.
FY18-19: 18.5 mill (lower end estimate, if you get 20, great)
FY19-20: 21+ mill, Pokemon Gen 8 + Animal Crossing (?) + Mario Maker + Bayo 3 + Fire Emblem + Metroid Prime 4 (?) + Star Fox Grand Prix + Monster Hunter Switch + Wario Ware Switch + DQXI + Switch Lite revision (12nm die shrink, less wide, lighter, better battery), price drop to $249.99. Peak Year.
FY20-21: 20+ mill, Switch Pro XL Mid-Gen Refresh boosts sales momentum ($300). Switch Lite price drop to $199.99. Zelda: BOTW2 (?), Luigi's Mansion 3, Mario Odyssey 2, Octopath 2, 2D Metroid, Final Fantasy VII Remake, Wave Race Rumble Storm, Elder Scrolls VI, Mario & Rabbids 2, Resident Evil 8.
FY21-22: 18.5 mill, still good momentum from Switch Pro like PS4 Pro and XB1 X are holding, 2D Super Mario Bros., Donkey Kong Switch (3D DKC), Fire Emblem Switch 2, Xenoblade Next, Pokemon Gen 8 Evolution, Monster Hunter Switch X, Dragon Quest XII, Street Fighter VI.
Would put you right around 96-97+ million LTD by March 31, 2022, should be able to cross 110+ million the following fiscal year.