Combining their home & handheld consoles into a single ecosystem and having Switch be the successor to 3DS & Wii U (along with being a spiritual successor to Vita) alone should get it to 80m.
Outside of that, Nintendo Labo could be the next Wii Sports/Fit, Brain Age, Nintendogs or Kinect type of hit among kids, families & casuals (20-30 million seller).
If Nintendo doesnt make any stupid mistakes than i think Switch can pass Wii.
When the herd loses its way, the shepard must kill the bull that leads them astray.