The EM plant is a direct upgrade from the Assembling machine 3 for a subset of products. It might make sense to make it depend on the Automation 3 technology. In my current game I'm able to research the EM plant, but not yet able to research Automation 3, since I haven't researched Speed modules yet. It would be possible for me to be building EM plants before I could build Assembling Machine 3s.
