Nolan on Superman: Good. He knows how to write a good story.
Superman going darker: Not good. Not every hero needs to go dark and Superman sure as hell doesn't suit it.
Mark Millar on Superman: Oh, HELL no. If I want the equivilent of a 12-year writing Superman, then we'll just get a 12-year old.
And frankly speaking, BlackCat, as the resident comic book geek and biggest Superman fan? I'm not crazy about Superman I & II as a whole. Yeah, they have some great moments, but the Krypton stuff in the first one go on way too long and is boring as hell. I tend to skip right to when he's getting to Metropolis. Superman II has great moments with the Krytonian criminals, but the final fight scene is stupidly disasterous. Of course, Superman II has my all time favourite movie moment, when he crushes Zod's hand.
Personally, my favourite rendition of Superman in any medium is the Animated Series. It has all the classic looks of characters and has some damn good stories; especially the ones surrounding Darkseid and Apokalips.
Honestly? If I were given similar control like Nolan, here's some of what I'd do:
-Skip the origin and leave it for the opening credits. Everyone and their dog knows it. Screw a full-on reboot. Let's do an origin reboot along the lines of Incredible Hulk.
-Metropolis is the city of the future because Lex Luthor, businessman extraordinaire, uses the city as his platform to test out the latest gadgets in various fields of science. Metropolis has a LOT of scientists; some employed, some unemployed, some sane, some not so sane.
-Part of the main story is an investigative report by Lois & Clark into these science-related activities, many of which they're finding are being tested through Intergang. And Intergang, headed by Morgan Edge (another corporate mogul) is in direct competition with Lex as they have a secret war within the city. Edge's main guy is Corban Dallas, who will be betrayed by Edge, barely rescued by Superman (blaming him for it) and volunteers for an operation at LexCorp to put his brain in a metal body powered by kryptonite.
-Kryptonite poisoning has Superman disappear while the city's crime rate skyrockets. Clark Kent goes home to Smallville, sick as a dog and recovering while Lois, of course, gets in trouble and investigates Lex a little too closely.
-Big finale includes not only Metallo publically going after Morgan Edge, but Lois in trouble at LexCorp.
-So, it wouldn't be a big city-wide threat but whether or not Superman can save the day with two things going on at once: stop gang violence from destroying the city thanks to Metallo...and Lex doing experiments on Lois for snooping. It ends with Luthor getting arrested, thanks to Clark Kent's expose through the Daily Planet.
This is a very rough draft idea and a lot of it just off the top of my head. Basically, I'd bring back the idea of Superman fighting mad scientists and mob bosses and mix it with some investigative reporting that we never really get to see in many Superman stories. Paul Dini and everyone behind the Animated Series said they wanted to treat Superman like a sci-fi action hero. And you know what? That works. Imagine a superhero version of the new Star Trek, with all the bright colours and cool gadgets (except, these ones are all used to kill Superman because he DARED to come to Lex's Metropolis and steal his thunder) Superman saves the day against Metallo, but Clark saves the day against Lex. I'd likely hint at other employees at LexCorp for future movies, such as John Henry Irons (who later becomes Steel), the janitor who becomes The Parasite, The Prankster, etc. Basically, a lot of LexCorp employees could be set up to become future villains.
And at the end of the credits, Lex gets released from jail of course, steps into his office and gets a memo about from his science team that they found a satellite orbitting Earth with strange alien letters. Lex is familiar with Kryptonian language. It reads "Brainiac".