Just looking at the front page: You will see that the gap (this year) is as follows:
PS4 vs Wii U: 7.9 - 2.0 = 5.9 million gap
3DS vs Vita: 5.1 - 1.6 = 3.5 million
Therefore logic would dictate that if this trend continues:
The gap between PS4 and Wii U will be more than 1.5x the 3DS and Vita gap.