Jez Corden from Windows Central said that he heard that Microsoft will have "quite a presence" at Gamescom. I hope it's more like Gamescom 2015 (a lighter, indie-heavy E3 with a few bigger announcements) than Gamescom 2017 (a bit of a bigger Inside Xbox without Phil and with minimal new announcements).
I personally would be happy with some Age of Empires 4 news, a Crackdown 3 gameplay demo (and at least some footage of the multiplayer component), some Ashen footage with a release date, and a few more indies getting a bit of screen time. I also wonder if Microsoft wouldn't have saved a smaller, Germany or Eastern European-based developer announcement for Gamescom just to give that developer's offerings some punch and give the acquired developer a bit of a showcase in their home area. If the rumors Microsoft isn't done making acquisitions is true, I think it'd make a ton of sense to hold one for Gamescom. There's a certain law of diminishing returns on new game studio announcements and holding one back during E3 to announce at Gamescom would be a good way to let people know more are coming and to steal headlines two months after E3. I've always wondered what Yager Development (Spec Ops: The Line) could do with more time and resources and they would seem to fit the mold of the studios Microsoft acquired at E3.
Other things on the "wish-list" would include a Battletoads gameplay teaser (although we have no idea where that game is at in production), a few surprise announcements about the game Vigor from Bohemia Interactive (I played it this weekend in Game Preview and it is really interesting, but I don't really understand the game or the motivation to make an Xbox One exclusive, Battle Royale light, loot and shoot game. I wonder if something else is up), and a cool, smaller first-party announcement (Perhaps another MSGP game? Crackdown will be out soon and the only other MSGP game we know about is Battletoads and they usually have a couple in the hopper.).