I like the idea of Lex being more of a supporting character and an emerging threat as opposed to being the big bad right off the bat and coming after Superman head on. I like the L&C, Smallville, and STAS type of Lex who's as important a supporting character as Lois Lane ,and who, while being up to something, is not always behind everything.
I'd first establish some of Superman's other foes and rogues, to establish that Superman has more enemies than just Lex and Zod, and that there are other threats in Metropolis which aren't connected to Lex Luthor or other Kryptonians.
Aside from Superman 3 , which had Ross Webster, Nuclear Man and Doomsday as a weapons, Steppenwolf who appeared in crossover films, the other Superman 1,2,4, Superman Returns, Man of Steel, Batman vs Superman, have basically exclusively featured Lex or Zod as the main villain.
I'd want to see foes like Intergang, Metallo, Livewire, Brainiac, Parasite, Toyman etc, first before building up to having Lex be the sole villain in a Superman film.