More compact and no more power brick. Why is it that that the PS4 is slightly more powerful yet comes in a smaller casing that also houses the power supply unit inside but the Xbox One doesn't?
Move USB ports to the front (x2) . The one on the side is a PITA in my setup.
Improve the controller disconnects...boggles my mind that this is still an issue and yes my controllers have all been updated.
Replace internal hard drive. External storage is great and all but I would rather have it inside the box to keep my system as clean as possible
Software:
DVR setup (but only if it allows full gaming while recording)
Support for Ethernet Tuners like the ones from Silicon Dust with full OneGuide integration
...or partner up with Silicon Dust and make sure they have a native app that works with SD'snew DVR platform
Allow OneGuide integration for 3rd party apps
Allow easier updating of apps (hear this is much easier on the PS4)
Improve snap interface/speed
De-App core services such as chat/party chat. I like the concept of apps but they can be cumbersome to do certain core things such as party/chat stuff.
More Dash customization/button press to see full background picture/screensaver that rolls through screenshots or picture folder via DLNA
Kinect improvements for setup and operation (since I moved it to the top of my TV, it seems like it's far less accurate for tracking and running the setup in that scenario is really lacking)
Beef up media app interface (basically make it more like Plex )
Built-in health check that suggests a restart when things aren't working right
Ability to schedule a console restart (i.e. normal operation is "Instant On" but say, once a week can have an optional full restart to help mitigate issues.)