In terms of software, Pokemon Gen 8 is their last big bullet left, since Zelda, Mario, Smash and Mario Kart are already available on the system. Of course we can see successors of the titles (except of Smash), but the impact on hardware won't be that much anymore. In 2020 and future, hardware will mainly be sold through price cuts and hardware revisions instead of new software.
Very difficult to predict the peak because of changing circumstances. If the new hardware revisions fly off the shelves like the DSlite, everything is possible the next years.
Don't released Animal Crossing neither 2d full fledge Mario Bros.
I don't think we'll get a new Mario Bros on Switch. We've already got a WiiU Port and Mario Maker. Next on the list is 3d Land/World esque game, either port or new. Though I'd prefer Odyssey 2.
Predictions (Made July 2019)
LTD: PS4 - 130m, Switch - 110m, XBO - 52m 2019 : PS4 - 15m, Switch - 18.8m, XBO - 4.8m 2020: Switch - 22m (Peak Year)