While Optimus facing the creators is obvious there are some writer backdoors that was left for other characters in a TF sequel. Namely Galvatron and Ratchet. Galvatron is Megatron but he lacks a Spark. Ratchet's Spark was extracted by Lockdown and his body destroyed. Now where am I going with this? The Creators wanting somebody to fight Optimus for them would give Galvatron Ratchet's Spark. The open Spark chamber could be something vestigial to Galvatron that Creators can exploit. Making him their slave. Ratchet's Spark being programmed for obedience or as a means of torture control like with Rampage or Tankor. Some speculated that Ratchet would be like the Vehicon generals like Tankor or Jetstorm. My theory is that it would be like Megatron-Ratchet of Marvel G1 when they were merged. Ratchet could pull a Tankor agreeing with Galvatron. But it could also lead Galvatron to have a conscience that redemption is possible like Prime Megatron.