Well technically, the PS4 CAN play PS3 games (and PS2 and PS1 games) via PlayStation Now. While yes, not an emulator in the form it's in, it's still capable to play the last-gen games. So PS4 just gained an advantage overt MSFT. PS Now is slowly coming to form and will be available to everyone very soon but MSFT? It's gonna take a while. Yup, I agree but if MSFT is just "considering" it right now, they'd better make it fast cuz Sony already's many steps ahead with it.
THIS. So Sony basically has the upper-hand now, in getting over the emulator problem. And the fact that they have GAIKAI in their hands means they got it all planned out. MSFT? Still at the considering stage so it's really gonna take a while.