Decades after the Kaiju Wars, it'll be all cyberpunk and dystopian, the opiate of the masses is watching the jaeger fights.
Suddenly, a new breach opens. Sport Jaegers have to be retrofitted to fight Kaiju. The story revolves around a down-on-his luck professional jaeger pilot proving himself as a warrior fighting the kaiju.
But the new Kaiju have a trick up their sleeves...
When the Breach was sealed, Gipsy Danger fell into the kaiju's universe. Though most of the jaeger was destroyed by the detonation of its nuke, pieces of it survived. The Kaiju learned from this and have come back to Earth with jaegers of their own.
Yes. Kaijus in jaegers. Huge, kaiju-sized jaegers.
Del Toro has already said that the sequel will involve a "merging of Kaiju and Jaeger". This is how I envision it.
Alternatively, it could be the precursors piloting their own jaegers, which would be an opportunity to find out a bit more about them. I would be okay with this too as long as we still got to see actual kaiju.
Or maybe even giant cyborg kaiju! :D
For the sea is dark...
...and full of terrors.