Just like he is in STAS, Superman can't touch him because he's got the law on his side .
Yeah, but we're forgetting that in the older comics, from the pre-crisis era, Lex was a criminal mastermind first and foremost.
It was only after the reboot of Superman by John Bryne that Lex became a leader in the eyes of the public, and got the law on his side.
I think it would be better set up for Lex to come back as more the criminal route this time. He could still be more in public, but he shouldn't have the law on his side.
Also, the fact that Superman doesn't touch Lex, isn't because the law is on Lex's side, it's because Superman doesn't kill humans. Plus, STAS Superman isn't canon. Only the comics.
But yeah, all in all, you don't need Lex Luthor, but it would be nice. Even a big hint would be fine.
Resurrected would be fine. I suppose having the clone be the one that got blown up wouldn't be bad, but having this new Lex be a clone, would be basically an insult to the fans.