Did you know that Metroplex was originally designed as a "Combiner"?
When Transformers proved an unqualified success, plans for a 1985 Diaclone line were scrapped, and Transformers was imported to Japan in its place. These aborted toys, which would have been part of a sub-line called Jizai Gattai ("Free Combination") were then incorporated into the Transformers toyline in 1986 as the Aerialbots, Stunticons, Combaticons, Protectobots, and Metroplex
Free-Combination is a special technique used by both Autobot and Decepticon combiners, allowing them to swap the component robots making up their limbs. It is different from Scramble Power in that it allows a certain level of autonomy to the individual robots, so that they can rearrange themselves when their unique skills are needed, forming special formations.
Metroplex was apparently designed as part of the aborted Diaclone line, Jizai Gattai ("Free Combination"), given the high degree of interactivity he has with other toys confirmed as part of it—namely, the Aerialbots, Stunticons, Protectobots and Combaticons. Each of the smaller "limb" robots from these four groups (and those that came after using their basic design, like the Technobots, Terrorcons and Seacons) can plug into ports in Metroplex's shoulders and knees in robot mode, while the base modes of the four leaders—Silverbolt, Hot Spot, Motormaster, and Onslaught—can connect to him in city mode. While the former feature was included in the Hasbro instructions, the latter was omitted (For the curious, Onslaught and Silverbolt use the slots on his knees, Hot Spot and Motormaster use the protruding slots on the sides of his legs). The peg-size of Metroplex's weapons also allows them to be wielded by the leaders (minus Silverbolt) and super-robots these teams create. This interactivity was played up greatly for his Japanese release, where he was part of the Scramble City sub-line.