I figured out a brand new approach to Transformers: The Movie, ignoring the death of Optimus Prime and even excluding Unicron entirely.
First, begin the movie with Hot Rod and Kup on Quintessa, this serves as a nice alternative introduction to the characters in a nifty little ‘cold open’ action scene, after they take a ship off the planet, we cut to just after the titles and see how Optimus and company are preparing to retake Cybertron
-The fall of Auotbot City Earth proceeds apace. Optimus is wounded protecting Hot Rod but his death is cut
-Shockwave, not Unicron, rebuilds Megatron and the other fallen Decepticons and turns them into Galvatron, Scourge, Sweeps and The Armada
-From there, play all three parts of The Rebirth