PS4: 119 million
I expect a PS5 release at the end of 2020. 79 million by 3/2018, +14 million the next fy, +11 the following, another +5 million until PS5 launch. Not expecting a lot of sales after the PS5 launch, as i predict a backwards compatible 400$ PS5, with the PS4 price not dropping under 150$.
XBox One: 51 million
Release of the next gen X-Box at the same time as PS5. Average sales per year in the 6-6.5 million range. Negligible amount of new consoles sold after NextBox release due to the budget market in the US beeing covered by used X-Box Ones from upgraders.
3DS: 75 million
Will probably beat the 72 mio prediction for 3/2018 slightly, but drop off completely afterwards with no more games releasing. Has overstayed it's welcome already, so basically no afterlife sales either.
Switch: See below.
LTD is basically impossible to predict, as we have no idea how long the Switch generation will last, and what kind of iterative upgrades they release. They could go for a straight successor after 4 years, or go for a longer lifespan of 6-7 years with 1-2 pro models and an entry level clamshell.
What I am willing to bet is that the peak fiscal year sees >25 million Switches shipped, it will outsell the X-Box One family before december 2019 and that my nintendo rewards will never be worth anything.
Edit: And if they release an oled Switch with Pokemon Joy Cons and a Red/Blue reimaging for the 25th anniversay it will become the best selling console of all time!