This is going to be so fun to look in couple of years.
PS4:100+m
Xbox: 35m
WiiU: 20m
Vita: 20m
3DS:70m
I don't think that MS will be interested on fighting an uphill battle after their initial attempts fail, they will probably bet everything on their Fortaleza glasses in an attempt to recreate what Kinect did last gen, Halo and Gears won't change their fate. I think that having to pay for Live Gold and PS+, people will be much less inclined to own both consoles. Better performance on multi-platform will become common knowledge with time, at that point the Xbox One will have to be priced considerably lower. Sony always does a good job supporting their consoles with good exclusive titles, I think it will payoff big for them this gen, they also have interesting things like good relationship with indies, PS+, F2P, Project Morpheus, PS Now, their promised IP TV service, remote play,etc.
I think the one year lead Xbox have last time combined with PS3 early years was crucial for the 360 success. Kinect also saved it from selling much considerably less than PS3.
Last gen 360 had a one year+ advantage to market(great advantage not only in sales but in building an online community), its was considerably cheaper for the entire generation, its had Epic and Bungie making games for it, its had superior performance on most multi-platform games, their Xbox Live was perceived as a superior product, Kinect gave it a sizable boost after its release. With all that Sony ended up ahead. If we look at 2014 sales PS4 has sold more than double compared to the XO, in a time where they had their biggest release of the year with am aggressive marketing captain and promotions, with all that it managed to beat PS4 for a week.