Going month by month is too specific for me, but here's what I think could happen during the year overall:
- F-zero game (FINALLY) with a robust online mode. Would be pretty sick. The "big release" for the first half of the year.
- Pikmin 4 w/online support
- NSMB Collection (collections seem to be the thing now, particularly on Switch. Would be cool to see a package featuring NSMB1, 2, Wii U, Luigi U, & maybe some all-new exclusive stages)
- New Paper Mario
- Earthbound collection (with Mother 3 Western release O_o) possible remake of at least one of them in the future, following the model of the Mana Collection
- New Donkey Kong Country by Retro to throw their fans a bone while we wait for Prime 4
- Mario Kart 9 (would likely be a pretty big overhaul/revamp to keep it feeling fresh like Super Mario Party - this could also be the "big" holiday release along with BotW 2, as Prime 4 is likely 2021)
- Geist sequel? I feel like Nintendo would want to round out the lineup a bit more with an exclusive FPS
- New WarioWare
- Maybe new Wario LAND? O_o
- New Rhythm Heaven (a chance this and/or WarioWare could be mobile releases)
- Another Ring Fit or 1-2 Switch type game that utilizes the HD rumble and motion controls
- GB/GBC/GBA game releases on the Switch online service
I feel like this is like 70% pipe dreams vs actual, feasible potential future games for next year but hey, a man can dream. And most of these I feel aren't outside the realm of possibility based on trends/conditions.