According to the moderators on the Vuforia forum:
You cannot detect arbitrary 3D objects, but you can detect 3D objects made up of planar image targets (e.g. a cereal box). Look for the MultiImageTargets section of the Developer Guide and the AR Extension for Unity 3 documentation (https://ar.qualcomm.com/qdevnet/sdk/unity/ar). You can create simple cube objects using the My Trackables system, or you can edit the config.xml file by hand to arrange image targets into the desired configuration.
A recent update allows Vuforia to track 3D cylinder targets.
The Sesame Street example was experimental and research is ongoing. There are no official plans to release it as a standard component of Vuforia yet.