PS4+XB1 is going to be ahead at the end. PS3+X360 actually lost customers to the Wii, especially during the first 4 years. This is easy to see on the first chart where the peak of the gap is at month 49, which was also Wii's last really good month. About a year later PS3+X360 starts to close the gap on current gen consoles. The Wii gamers started to transition over, but not all of them made the transition. So PS3+X360 ended up behind PS2+XB. For the same reason I think PS3+X360 will also be behind PS4+XB1.
The Xbox 360 had 8 years on the market before the Xbox One launched and PS3 had 7 years before PS4 launched. Looks like PS4 and Xbox One will have 7 years to themselves before their successors launch this holiday season. I do think PS4 and Xbox One will beat out PS3 and Xbox 360 in the end. But not by a lot. Less than 5 million.