While I think that windows 10 needs a rebranding as WinX, its package of Dx12 and seamless streaming of Xbox is mouthwatering. Plus Microsoft is going to release an adapter to use the Xbox One controller wirelessly with your PC.
Other than above-mentioned goodness which is on the way in 2015, what makes me happy is the fact that I might see a subtle harmony between a console, a pc & a Augmented Reality (Microsoft Hololens).
During 2015 If Microsoft starts to syncs all 3 devices (PC, Xbox, Hololens) in such a seamless way that our boundaries of each hardware start to fade then it will be an achievement. Because I see a great potential in turning this trio into an irresistible service offering rather than each serving as separate hardware.
Plus I’d like my PC to stream to MS Hololens, so I can start playing Dota2 in Augmented Reality & cast spells with cool custom hand gestures or may be use wireless controller. So that’s that. ;D