I'm optimistic and a little skeptical at the same time about whatever the Man of Tomorrow will be, as it seems the way Gunn put it, it's not Superman II.
More about Lex and his backstory? It might be good though. I would want to explore some of the good in Lex. I'm speculating Gunn might included...Lionel Luthor? I think I remembered Gun saying he called Lexcorp, "Luthorcorp" instead because it opened room for Lex's father to appear? Not that it might be the name 'Lionel'.
I would like to see Lex try to earn the people's trust back in some way or make it seem that he really believed he was doing the right thing because he really saw Superman as a threat, so he wants to earn people's trust back...by running for president. Actually I don't like that idea because in this context, it wouldn't be believable. Lex couldn't be trusted again. There's no way. At least not that soon after the events of splitting the Earth open. Probably never. Unless Lex figures out a way to brainwash people that might make him look innocent. But not literally brainwashing because that would be disappointing, but in an effective way.
If Lex is the main character, but Superman is a strong supporting character, that will either work or not work. As long as Superman has-let's say equal screen time? If you think about how 'Superman' was portrayed in 'Lois and Clark' (Okay let me get this out of the way first: I absolutely despise Dean Cain)
I don't want to make this comparison, because it's not like I know how it's going to be. What if the film uses the 1984 film, 'Amadeus' as an inspiration? Where Salaeri was the actually the main character, even though it felt like Mozart was the heart of the movie, which he was. He kind of was the main character.
So if Gunn is going to delve more into Lex Luthor's backstory, I hope he establishes some of his lightness. Showing his interest in classical music. More of his clever puns. His interests in Roman and Greek history. (Kind of got that already in that one scene near the end of the movie though)
I can't imagine how much of Lex can be explored though. This is a more serious take on the role than Gene Hackman's portrayal. Have to admit, despite Hackman's version being kind of goofy, Hackman was hilarious. I always loved his insults with Otis. The slight problem I had with Hackman's Luthor was that I couldn't take him seriously enough as a villain or as much of a threat to Superman, but not completely. Hackman still proved to be mostly a threat to Superman in the end. Hackman's Luthor always had a plan. On the whole though, Hackman's Luthor had so much personality and it feels like he would seem more interesting of a character to delve into more than Hoult's portrayal, even though, I do prefer the post-1986 version of Lex Luthor. Hoult's Luthor is downright more serious though.