The post in question was written by the head of the Xbox MVR team, and it focused on the changes coming to Xbox Music (and how it would look on Windows 8.1), but almost as an aside the post happened to mention that Xbox Music was one of the projects being developed by the Xbox MVR team.
I think they just gave us a hint just how much Microsoft cares about ebooks, and I think we now have a second explanation for why MS invested $300 million (plus a promised $300 million) in Nook Media last year. Of course, B&N had already indicated that MS would launch ebookstores in 10 countries but now we have an idea which team at Microsoft is doing the work.
If I am right then this is a sign of a second parallel ebook effort inside MS. In addition to the new Reader app for Windows 8 which is being developed by the Office team, we now have a hint that there is also an ebookstore under development by the Xbox MVR team.
My source thinks that this might be a sign that MS is going to release a handheld reader of some kind, but I'm not so sure. Remember, this hint came from a post about Windows 8.1, which tells us that the Xbox MVR team develops for Windows as well as the Xbox.
But I could be wrong. There have been rumors in the past that indicated that Microsoft's future Xbox might have a 7" tablet style controller similar to the one found on the WiiU, but aside from a leaked and possibly fake spec sheet all we have are rumors. That device was called the Xbox Surface in the rumors, which of course means nothing.
If that Xbox Surface (or something like it) does show up then we'll probably find that it has an ebookstore, but I also don't expect to see an ebookstore on the Xbox One. I'm not convinced that anyone will want to read for any length of time on their TV screens.