Update: Microsoft's Xbox Live programming head Larry "Major Nelson" Hryb has confirmed that the Xbox beta app for Windows 10 is now available, adding that it "includes real-time activity feed in friends list."
Although the app was available for download, it was continually crashing, and we found that the version number was older than that of the stable Xbox app. That's changed with the update, with Xbox (beta) now at 9.9.21000 while the stable build is at 9.9.16003.
Interestsed in taking a look? Hit up the link below to get started.