I think it's definitely possible. While there are still a lot of 360 owners out there, the most active and hardcore have moved on to the XB1.
Lots of people thought Gran Turismo 6 was gonna sell really well on the PS3 because of the huuuge install base. Turns out that wasn't true, because millions of the hardcore crowd had already moved on to the PS4, like me. It was the first Gran Turismo I didn't buy.
For whatever it's worth, Titanfall on XB1 is currently 13th on Amazon's Top 100 videogame charts. The 360 version isn't anywhere in the Top 100. This 2 week delay has nothing to do with that.
There hasn't been a single cross gen game that's even come close to outselling the last gen version. And yes, gt6 tanked, but it still sold far more than it would have on the ps4. Look at forza 5 sales.
The hardcore preorder games. The Amazon top 100 has never been a good sales indicator beyond what the hardcore are buying. It certainly doesn't match up with the npds.
Also there is a slight amount of risk in this move. Everyone is assuming that the game will be universally loved. I think it will be also. But what if it isn't? What if xb1 and pc players hate it and spend two weeks trashing the shit out of it before it releases on the platform it's going to sell the most on?
I don't think that will be happen, to be clear, but Microsoft is taking a risk here.