If you export .obj animations you get a sequence of .obj files containing the mesh in its poses during the animation. Is it possible to tag, say the shoulder of a mesh, so you could dig into the exported files in say jme3 and attach other meshes (arms eg) to that location? You could. eg, select the shoulder vertices and give them a property in the logic panel, but how would you grab the info from Blender to rewrite the .obj exporter? Either that, or is it possible to get the .obj exporter to export empties and their location… I know Ogre does.