With the reboot, an all new cast is expected of course. But had Bryan Singer ever made a sequel to Superman Returns Kevin Spacey would have been back on board as Supes' greatest nemesis Lex Luthor. Many fans are very happy said sequel never materialized, but Spacey sounds like he is still up for another go round as the iconic villain. While speaking to Screenrant at the Press event for Casino Jack, the actor offered the following..

“They haven’t called. All I hear is what you probably hear too. All I know is that when I hear a reboot, I assume they’re going to recast everybody. But, yah, in principle, there was already supposed to be a second one but it never happened. It’s their option. But I had a blast doing it. My suspicion is they’re going to reboot the whole thing.”
“I’m a huge fan of Bryan Singer’s. I thought the movie did pretty damn well. It’s always one of those things where because it’s such an important franchise to so many people, and they’re so devoted to it, that you’re always going to end up with people who didn’t like it or liked it or liked (a certain) part.”
Your suspicions are correct sir. Its highly doubtful Spacey will be getting that call. But then we are not even sure if Luthor will feature in the new movie at all. Do Spacey's comments confirm that he will? Doubtful considering he seems to know quite a bit less than we do about it already. I think most can agree, even if other elements of Singer's film disappointed fans, that Spacey portrayed a pretty good Lex Luthor. I would have liked to see where he would have taken the character in future movies. Evidently so would he.