I considered SG Drift as another limb, but I was hoping for different molds for each limb...not really sure why come to think about it since Takara's plan for their combiners involves a lot of repaints/minimal remolds. The chest-piece idea is brilliant though.
Either way, Hasbro is totally missing an opportunity with their choices for their Fan-built combiner. C'mon Hasbro...where's Driftotron?