If Nintendo releases the right games, the Switch should have no issues matching and passing the Wii and DS in total 10 million sellers.
I even thing it could catch or pass the DS in total 20 million sellers. the DS had 3 games that broke that mark, New Super Mario Bros. Nintendogs, and Mario Kart DS. I think MK8D and Super Smash Bros. Ultimate should reach that milestone, no problem. Super Mario Odyssey could do it to if it can maintain solid legs. Breath of the Wild could probably even do it.
Hardware Comparison Threads:
Current Thread
Is Hardware Getting TOO Powerful?
Older Threads:
PlayStation/Xbox/Switch: 2022 Edition
PlayStation/Xbox/Switch Hardware Battle: 2021 Edition!
PlayStation 4/Xbox One/Nintendo Switch: 2019 vs. 2020
PlayStation 4/Xbox One/Nintendo Switch: 2018 vs. 2019
PlayStation 4/Xbox One/Nintendo Switch: 2017 vs. 2018
PlayStation 4: 2015 vs. 2016 vs. 2017