They finally have a writers "room" to craft some cohesive story for the next three Transformers movies this decade, and beyond. Here's origin story number 5 involving Earth and Cybertron according to the latest rumor
Transformers: The Last Night will involve Optimus Prime finding his home planet, Cybertron, now a dead planet, which he comes to find he was responsible for killing. He finds a way to bring the planet back to life, but in order to do so he needs to find an artifact. And of course, that artifact is on Earth. What is that artifact? Well, here’s where things get weird.
Somehow the artifact ties into Merlin, the magician of King Arthur lore. Apparently, the power of magic was given to Merlin by a Transformer and somehow the artifact ties into this.
If this is true, doubtfully Spielberg would use Excalibur again for Indy 5.