I am assuming these predictions are consoles sold-through to consumers for January 1st 2018 to December 31st 2018.
(Wish we had more knowledge about 2018 to make better predictions...)
Nintendo Switch : --- 21.1 Million
Playstation 4 : ------ 17.5 Million
Xbox 3 : ------------ 6.5 Million
3DS : -------------- 4.0 Million
Vita : -------------- 0.2 Million
Wii U : ------------- 0.0 Million