I can't remember who asked about this at the London meetup but options are:
.X3D seems to be trying to become the web standard. We would want to modify it a bit to support our preferred video and audio formats.
.blend Native file format of blender 3D rendering software. Covered by various versions of GPL. They also make films. The latest, Tears of Steel, is not on commons because even the low res versions clock in at over 300MB. The 4K version is a bit over 6GB. In any case their films can be found on the usual video sites.
.Blend would perhaps be best treated as a raw data format with the renderings exported to something else. On the other hand blender is probably the most powerful free and open source tool for 3d work.
From the 3D printing world we have .STL and .AMF. If supporting printable
objects is our prime interest they would be the way to go.