I think it will be based alot on Birthright, and will take a cue from BB and TDK.
Some of this is borrowed form bits i've read over the years, other parts are my own.
My idea film would be to have Brainiac as the main villain..Zod and ursa would be shown on Krypton only. Zod is jealous of Jor-el's achievements and he creates Brainiac out of spite. When Zod presents Brainiac to the council, it is rejected.
Zod throws a tantrum and he and ursa kill most of the council members.
Realizing what he has done, and fearing for his life, Zod programs Brainiac to destroy krypton. He then plans for he and Ursa to escape. Before the end, Zod's hatred of the EL's is somehow accidentally downloaded into Brainiac. That act causes Brainiac to become sentient. Brainiac kills Zod and Ursa then escapes the planet in their ship.
Two spacecraft are seen leaving the exploding planet. Both craft carry life that has just started..one carries Krypton's last son, the other a cyborg/computer. One craft heads to Earth, the other to God knows where.
We would see Clarks arriving at this point, his growing up in smallville, traveling the earth before becoming Superman, getting his job at the DP, And his first encounter with Lex.
Many, many years later, after visiting several other planets and leaving them in ruins, Brainiac tracks Kal-el to Earth, where superman is already established and has history with Lex. Brainiac has created a Large spacecraft and several drones of himself..each almost as strong as the original, and each just as strong as Superman.
Brainiac attempts to defeat Superman with the drones..big fights over several countries, lots of damage and destruction. So far superman holds his own and defeats a few of the drones, but he is starting to weaken from the constant fighting, and gets knocked down. They swarm him.
Lex is at first giddy to see Brainiac getting the best of Superman, but when he realizes that Brainiac might actually win and then take over the Earth himself (or destroy it) Lex intervens. It would be a 'the enemy of my enemy' sort of thing.
Maybe Parasite, Metallo, and Bizarro will exist in this film..It would be something to see Lex send them to aid Superman..weird, but still kool.
I think with Snyder directing, anything is possible.