I'm putting a pin in this post to see how long it takes, if it happens at all.
Things can change, but as of this writing, it's clear the XB1 has no momentum in the wake of the release of its halo/flagship game.
I think the XB1's fortunes can be shifted with a $399 SKU paired with an exclusive MS Studios release. I'm thinking Halo 5. If MS does a $399 Halo 5 Limited Edition bundle with a hardware refresh (facilitated by a cheaper BoM cost and possibly w/o Kinect 2), that could be a game changer.
The question is whether MS will be able to do this in time within the first year of release. It's already looking like the PS4 will cross the 10m units to consumer hands milestone before that point and will have flexibility of their own to both reduce BoM cost (it's already being done as I'm writing this) and MSRP of the main SKU in response to any price cuts by MS.