Today, Microsoft will be releasing a new Xbox One Insider Preview build to the Preview Alpha ring, marking a significant milestone for the version 1910 feature update. According to the company's Brad Rossetti, the update is now feature-complete. Today's build only contains a bunch of fixes.
Unfortunately, the actual features will be announced next week. Oddly enough, while version 1910 has been in testing with Xbox Insiders for some time now, Microsoft really hasn't talked about many new features. The two things that we actually know are coming is that the Dashboard will be redesigned, removing the tabbed interface, and that Cortana will be removed from the Xbox One console, still allowing you to control it through separate Cortana devices.
Other than that, any new features that have showed up have ended up in monthly updates that are already in production. If there are indeed new features that haven't been spotted, we'll hear about them next week.
As the 1910 version number indicates, this feature update should ship in October.