It's still unclear about the wii u. It's still struggling but Nintendo have lots of cards to play like price cutting. It's a very cheap console to make. I think the lowest it will do is something like 22 million. However it could easily be turned around and do 50-60 million as the casual console choice again. I don't see it doing wii numbers.
The 3DS is harder to work out because we don't know when it will be replaced. A new improved model could come out with 3DS backwards compatibility and that won't count towards 3DS sales. Nintendo do revamp their handhelds quite frequently. So Nintendo themselves may limit 3DS numbers by replacing with something better.
I think the PS4 will do huge numbers. It's a fantastic product, very stylish, very powerful, highly desirable and a great price but there isn't a lot of software currently. I think next christmas will be when we see huge numbers. Sony keep selling the same hardware for a long time. The PS4 will probably continue being sold into poorer countries many years after the PS5 has come out. I really think its going to do some huge numbers. Somewhere between 100-150 million. However that figure may not be reached into 2020 or beyond. Also the PS4 may get integrated into other devices like televisions. It's possible a ps4 design without optical drive and reliant on flash memory rather than a physical hard drive becomes integrated into other devices. It's already quite a simple motherboard. A few later generations in fabrication process for the silicon will make it very low power and cool running. Faster internet connections will allow full games to download quickly. Sony will want to get more people using PSN and buying downloads. I also think by integrating ps4's into televisions there will be ways of improving input lag and much smoother visuals with the ps4 using something similar to nvidia's g-sync.
