Why would Wii U sell 6 million next year when only sold around 3 this year, a year with its biggest franchises?

PS4---20.5 m

PS4 will surpass the 20m units sold per year. The more it sells, the more people will choose it over the XBone. If they made online free it would effectively murder the XBone in cold blood, but that won't happen.

XBone--6 m (1,5m with Halo bump)

XBone can't effectively compete with PS4 without a lot of investment (pricedrops, bundles, timed exclusives...), so the gap between them will continue. The only significant bump the XBone will get is Halo, before and after Halo the console will be constantly pummeled by the PS4.

WiiU---3.5 m

WiiU has used all of its big guns, so the weekly sales will be healthy enough to repair the losses of the first year, but without any significant benefits or spectacular sales. WiiU might sell more, since it already has a steady library, though. This console will have the most stable sales of all.

3DS----7.5m

I suppose the next year would be the real test of fire for the 3DS, XBone and WiiU. 3DS has the N3DS coming to the west, but has no system-seller (Even Youkai Watch probably won't make a big difference in the west). The most optimistic prediction for 3DS is selling as much as it did this year. I hope Nintendo keeps the handheld alive until 2018, but that is too optimistic.

Vita---1.2m

Vita might surpass the 10m units by the end of the year, China won't be interested in the handheld when they are used to mobile. Sony won't make anymore AAA or AA (or even A) exclusive for the console when they can put it on the PS4 or PS3 and sell way more.

The last gen consoles sell well enough to keep its price. Maybe at the end of the year the Wii is finally discontinued, but I'm sure the console is really cheap to produce, and it makes a small profit, enough to keep the system alive.

So, the Xbox One will sell less next year compared to this year, despite the high probability of a lower price throughout the year and their biggest exclusive dropping in the holidays. I wish you the best of luck with that prediction coming to fruition, because I simply don't see that happening. 

The rest of your numbers seem reasonable though.