Insider NateTheHate reported that Microsoft is preparing a game based on one of its owned franchises. Microsoft will be the publisher, and development will be handled by a studio not part of Xbox Game Studios. However, the insider denied rumors about Banjo-Kazooie, The Elder Scrolls VI, Wolfenstein 3, Blade, OD, Fallout remasters, and a StarCraft shooter.
Windows Central journalist Jez Corden also stated that it is an unexpected sequel, and its announcement will be a big surprise. He continues to look for additional information.
Moreover, I'm working on a serious rumor that Xbox will also announce one or more games at Gamescom. Usually, Microsoft saves full announcements for the Xbox Showcase in June, but this year, it seems they have planned some real announcements for Gamescom as well. I'm not sure if they will appear at the Xbox show or Geoff Keighley's Opening Night Live, but if what I've heard turns out to be true, we might be in for a big surprise (likely a very unexpected sequel) (not Banjo, lol).