They will make money on this. Even if they only sell 1M Xbox PCs, with a margin $100-300 a box, that's $100-300M of profit just on the box. Their main money will come from selling Minecraft, COD, Diablo, the next Elder Scrolls as a 3rd party publisher.
In today's market conditions, making money selling hardware is practically impossible. Unless, of course, they set a market price based on the cost of components, but then no one will buy it (the price tag is unlikely to please). Typically, such hardware is sold at breakeven or negative at launch, to build a user base.
Minecraft, COD, Diablo—these brands are currently generating revenue for them, but as we can see from their financial reports, it's not helping them much, for a variety of reasons. So far, Activision - Blizzard's acquisition of has been more of a negative than a positive, and according to recent news, we may be saying goodbye to several more studios this year (possibly). So, again, it's unclear why this should suddenly turn into a profit if they can't do so now.
Elder Scrolls - Let's wait for the release, otherwise I have a feeling I'll have grandchildren before this game comes out.
3rd party publisher – again, there are so many publishers on the market, it's completely unclear why everyone should suddenly abandon other publishers and rush to Microsoft. To do that, they would have to offer better terms than others, which they don't yet have.