It doesn't have to beat the 3DS at all. I think if it sells 6 or 7 million a year that is enough to be successful.
But, personally i consider it successful now as it gets a decent amount of support, especially from indies.
Xbox One, PS4 and Switch (+ Many Retro Consoles)
'When the people are being beaten with a stick, they are not much happier if it is called the people's stick'- Mikhail Bakunin
Prediction: Switch will sell better than Wii U Lifetime Sales by Jan 1st 2018