Around 60 to 80 million, similar to the 3DS.
On one hand, I was confident that a platform like the Switch would attract some of the best support from Nintendo's previous systems. Enough DS and 3DS XL's had been sold to convince me that an oversized handheld was not a major issue, and I was confident that Nintendo's mainstay series on consoles would sell in line with previous entries. My thoughts were "New 3D Mario and Smash are going to sell 10 million, Zelda will sell 7+ million, Pokemon will sell 15 to 20 million. So somewhere around 3DS levels sounds reasonable."
That said, I really didn't expect the degree to which games like Super Smash Bros Ultimate and Breath of the Wild would be much more successful on the Switch than on previous consoles. I predicted that Pokemon, Nintendo's handheld fuel, would take longer to develop new games on Switch, which ended up not being true. I also underestimated the degree to which third party developers, both indie and major, would be willing to port games to the Switch, even if these games are often practically ancient.
Love and tolerate.