Star Trek 4 should look at a key plot point from the Kelvin films.
During the events of Star Trek: Into Darkness, we’re introduced to Admiral Marcus, played by Peter Weller (Robocop!). During the events of the movie, we find out that Marcus is attempting to turn Starfleet into a more military-oriented outfit, and is attempting to do so by starting a war with the Klingons. He does so by sending Captain Kirk on a suicide mission to the Klingon homeworld of Qo’noS (Kronos) to retrieve John Harrison, aka Khan Noonien Singh. Marcus woke up Singh to help him create new weapons for Starfleet, and after Marcus realized he couldn’t control Khan anymore, the events were in motion to start a war with the Klingons.
Purple Power Ranger-looking monsters aside, it was a really intriguing idea. Set up the Federation by having one of its most well-known Captains, James Kirk, land on the Klingon homeworld to look for a former Federation asset gone rogue?
A solid way to start a war. And for all intents and purposes, it should’ve. The Klingons caught Kirk and Khan, which resulted in Khan killing a dozen or so Klingon soldiers. At some point, they’d have to know the Federation was involved, and that would have more than likely triggered a war with the Federation.
That war is something that needs to be explored in Star Trek 4
While Star Trek: Discovery explored the Federation and Klingon war to a degree, it didn’t do a great job and turned more fans away from the product during the events of the first two seasons of the show. So a lot of fans still haven’t seen a well-done Klingon/Federation war.
Setting the fourth film against the backdrop of a Klingon invasion of the Alpha Quadrant would be really intriguing and while it may not have been that long since the last time they did a similar story arc, with the correct writer, the fandom may finally be able to explore a high-concept like a Klingon/Federation war.
It’s not the only war idea that the film can explore, but it’s the one that makes the most sense when you look through past films of the Kelvin Universe.