My Colleague is working on the windows native stream of our products and is currently working on pushing all the geometry into a single interleaved array for batching.
He will have all the geometry stored this way. This seems very efficient, he said its an extension of vertex buffer objects. Is there anything similar in Jme for pushing all geometry's into a single object?
well, if u want u can attach all the geometry to one single root and maintain that root only.
but it really makes more sense to attach the geometies based on their scene graph representation.
im not really sure this will slow down the game, but from what i have seen, scene graqph representation is really effient. 
jME currently does not support interleaved arrays.