Okay, admittedly, Cavill leaving hasn't been confirmed yet. But it definitely is a possibility. So if he does indeed leave and the Big Blue gets another reboot (or soft reboot or revamp or whatever), what are you hoping to see in the next Superman movie or movies.
In terms of new actors, I'm actually kinda hoping they skew young with Superman. Maybe someone in the 25-30 range. There have been plenty of origin stories for Superman on-screen but we've never actually seen a visibly 'young' Superman other than Brandon Routh (and he was supposed to be playing the experienced Reeves version). I'm hoping for an actor who could embody the New 52 Superman from Morrison's run, or the Superman from Earth One or American Alien.
Granted, they may not be able to go with a Superman that young if they intend for the new version of Superman to co-exist with the Supergirl (and chances are the Supergirl movie will be out before the next Superman one). Though I'm kinda hoping that the next Superman movie will be an 'early years' film ala Matt Reeves' Batman film, from what we've heard of it.
Now for the story - The early part of the movie would show us Superman operating in Metropolis. He takes on organized crime, particularly Intergang, but he also clashes with corrupt and exploitative businessmen and politicians. Basically, there's a dash of the Siegal/Shuster Superman in him, albeit updated to the 21st century of course. The authorities are vary of him, but many cops - particularly SCU officers Maggie Sawyer and Dan Turpin - view him as a hero, as does the public. In the meantime, as Clark Kent, he's an investigative reporter tirelessly fighting for the disenfranchised, and enjoying a friendly rivalry with Lois Lane. Oh, and both the Kents are alive in this version, and we see Clark with them at the farm on occassion, discussing how he feels about his role as Superman and his worries that he may be going too far sometimes.
The plot gets kicked off when Lex Luthor makes contact with Brainiac after a LexCorp satellite picks up one of Brainiac's drones, who is aware of who and what Superman is. Luthor 'invites' Brainiac to earth, hoping to use Brainiac to get rid of Superman, who's actions have been affecting his illicit dealings and his stranglehold over Metropolis. Brainiac however arrives intent on assimilating earth's knowledge and then destroying it, as it has countless other planets. Brainiac steals several cities by 'shrinking' them into pocket dimensions based in bottles, and Metropolis gets shrunken as well. Superman pursues Brainiac's ship but gets captured and placed in Kandor.
The rest of the film is a powerless Superman finding a way to escape Kandor with the help of a scientist there (an old friend of Jor-El and Lara's), and then regaining his powers in time to stop Brainiac from destroying the earth, and thus cementing himself once and for all as earth's greatest hero.
I think a story like this would be perfect when it comes to showcasing Superman both as a crusader of the people and also as the world-saving hero who fights against sci-fi threats.