As we reported about a month ago, The Khronos Group has finalized glTF 2.0, which is a 3D format designed for whole scenes. Since then, Khronos have published an exporter for Blender that implements what appears to be all core features, as well as specular-gloss PBR (Extension), lights (Experimental), “materials common” (Experimental), and “materials displace” (Experimental). It is implemented as a whole bunch of Python scripts.
Apparently they provide their own PBR shader nodes for Cycles, rather than using the new Disney-based one in Blender 2.79. I’m not sure whether this was to make the export easier, or if development schedules just couldn’t align. Either way, both metallic/roughness and specular/gloss workflows have been provided, so that should make exporting either workflow relatively straight-forward.