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.
One AAA 2D Mario bros. maybe rise 20 M sales