Aren't screen space reflections only suited to smaller indoor areas? And how would you use a single cubemap work for all the different reflections?Cubemap would be used only if screenspace does not contain valid data. Sky box would be good candidate for it.
It does no matter much if the area is indoor or outdoor because everything is gathered from screenspace so relative distances does not matter.
There is quite good picture comparion showing the effect in outdoor scene http://blogs.amd.com/play/2012/06/06/fast-and-beautiful-the-directxÂ®-tech-of-nexuiz/