Microsoft confirmed that the Xbox One S will not give the games you already own a power boost.But powerful Project such as Scorpio might.
Phil Spencer:"If you look at a game like Halo 5, it implements something called dynamic scaling.As scenes get more complex, in order to maintain 60 frames per second, they will actually change the resolution that you're running at, and they're not the only game that does this. So if you run that game on Project Scorpio you're actually going to be at the max frame rate of that game more often."