Anhas dug up an XML file within the PC version of Gears of War: Ultimate Version, which lists several interesting possible titles coming to the Windows 10 store.
The big names on that list are Scalebound, the dragon-rearing action game from the makers of Bayonetta, and Forza Horizon 3. The former had not yet been announced for PC, and the latter has yet to be announced for any platform.
Both these titles would make total sense on Windows 10, given Microsoft'sto focus on cross-platform development.
Are these just placeholder listings, or do they indicate active development? I'm sure we'll find out one way or another soon.