This isnt about how many total sales each system will do but moreso about how they will do each individual year. Wii had a traditional 5 year sales curve where it built up momentum and peaked in its 3rd year then had a gentle decline for the next few years, on the other hand PS3 and 360 started off slow and and peaked much later(PS3 due to price coming down, 360 due to Kinect giving it a second wind).

Wii U-right now were seeing a slow start mostly because  many of its games have been delayed. I believe that will all change later this year with a potential price cut and big 1st party games like Wii Fit/Party, Pikmin, Wind Waker, Mario Kart plus solid 3rd party multiplats, all in all we should see 6-8 million Wii U sold this year. That momentum will continue into 2014 with heavy hitters like 3D Mario (Q1), Smash Bros (Q2), Metroid (Q3), Zelda (Q4) for a total of 12-15 million Wii Us sold 2014. 2015 coulf see sales start to decline but a price drop to $199 and games like New Super Mario World and Nintendo Land 2 keeps sales high, 10-12million this year. The next few years will likely see a steady decline, 2016 7-9m, 2017 5-6m, 2018 3-4m.

PS4/XBOX-these consoles will likely have a solid launch but 2014 will have a slow start, $400-500 price tag+majorit of games available on PS360+Wii U gaining momentum being the reasons. I see Xbox doin 6-8m and PS4 7-9m. 2015 will see a decent gain in sales as games start showing off the next gen power and fewer games being released on PS360 plus this could be when they recieve there first price cut, both could be around 10-12m this year. 2016/17 is when i think they will peak, PS360 will basically see support dry up, Wii U beginning to decline and reching sub $300 price tags. Sales for these years 12-15m each. 2018-2020 will see steady declines much like Wii U in 2016-18.

Overall I see Wii U having a similar curve to Wii but closer to PS360 yearly sales and PS4/Xbox having similar sales to PS360 as well but peaking 1-2 years earlier since PS4 should reach $300 sooner than its predeccessor and Xbox not having a mid gen upgrade to boost sales so late into its life. 

I can see with Nextbox/PS4 being in a WiiU type situation for awhile because of their high price tags. I think both 360/PS3 see price drops this year and that entices many to buy those instead.

Next year they all 3 sell more. I think WiiU finishes the generation last, I think MS a good 2nd and they dominate in the US and profit the most. PS4 "wins" the sales number battle thanks to Japan and other territories MS is basically non-existent in.

I think Nextbox and PS3 both sell 75-85 million, WiiU well below that. I think Nintendo will quickly reach a point where they just need to launch a new console. The WiiU is just too similar to the Wii.

Wii U: No price cut this year. The core Nintendo games will come out late 2013 - early 2014 but third party support will never be there, leading to a modest upswing finishing at 20-25m units worldwide and peaking in 2014.

PS4: Day1 spike but not Christmas spike. The price will be too high to justify the very small number of PS4-only exclusives, when most games especially third party will be available on PS3, and some like GT6 will be PS3-only. 2014 will be very slow as third parties avoid next-gen exclusives. 2015 is when we will see the first games that don't release for PS3/360 as well, and it will recover much the same as the PS3 did but never to the same pace as the price will come down much slower due to lack of technology.

720: Similar to PS4 but lower. Kinect and associated games will fail to sell as long as it's >$300. Even fewer exclusives/reasons to buy than PS4 because of weak first party support and third parties even more strongly attached to 360/Live. Particularly very low Live subscriptions until Halo comes out in late 2014.

Both systems will be on the market for six years. MS and Sony would prefer 7+ but sales are so weak that they are cancalled sooner.

Wii U will be replaced after four years on the market with something completely different.

We seem to see eye to eye on most things except I habe a little more faith in Wii U. 2nd half of this year thru 2015 should be pretty solid for it, PS4/Xbox will be priced much higher and in direct competition with PS360 while Nintendo will have its core fanbase, casuals (not nearly as much as Wii but still a solid amount), people looking for a 2nd console. I think Wii U will sell around 50m lifetime and have a successor in 2016-17, possibly a console/handheld hybrid "3rd pillar" that will coexist with WiiU/3DS for 1-2 years then become the sole Nintendo console.

I agree with PS4/Xbox and expect them to do about PS4-80m and Xbox-70m. Xbox having the NA/UK market while PS4 has Europe/Japan/Other and both seeing a successor in 2018-2020 but most likely 2019.