end of 2013 sales will likely be 5.25m for Wii U and about 3.75m for PS4 so Wii U has about a 1.5m lead to start the year.
Q1 of this year will likely be better for Wii U than it was last year due to more improved library, cheaper entry point and a big hitter in Donkey Kong Country. According to Vgchartz Wii U sold about 600k from Dec 30 2012-Mar 30 2013 so I could see it doing between 750k-1.25m in Q1 putting it in the 6-6.5m range. Then in the Spring Mario Kart releases which will be big so I could see another 1-1.5m being sold by the end of June which would put it at 7-8m.
PS4 will still likely have supply issues in the west and is launching in Japan in Feb. Sony is forcasting 5m shipped by the end of Mar but we dont know if thats how much they can manufacture or if its a lowball number so they can exceed expectations. Ill say it will have sold 5-6m by the end of March. By Q2 the stock issue should be solved and it will have launched in all regions so we will start to see what its baseline sales are. Assuming that PS4 averages about 150k per week that would give it 2m for the quarter and 7-8m by the end of June.
By the end of Spring I have Wii U and PS4 both in the 7-8m range so PS4 may or may not pass it by then but either way it wil be close. PS4 will have soundly passed it by the end of the year though.
When the herd loses its way, the shepard must kill the bull that leads them astray.