I don't know if the people who buy ps2 and didn't buy a ps3 goes to xbox if it's the case i expect that this people will back to ps4
PS4 - over 100 millions let's say 120m
Xbox One - 70m
Wii U - 25m
Vita - 15m if it will not get Final Fantasy Kingdoms Heart and Monster Hunter 20m otherwise
3DS - 80m