DC's announced but not yet detailed "Rebirth" initiative. It's not unreasonable to think that "Rebirth" will be more than just a marketing initiative, and will, in fact include some in-story way to bring an official close to the New 52 DC Universe, which launched in September of 2011.
The launch of the New 52 was a reboot of DC Universe continuity that lead to what was, in practice, a sort of half-assed line-wide equivalent of Marvel's millennial Ultimate line (That is, a reboot that re-designed the characters and started over with them...only, in DC's case, they didn't start from scratch, but introduced readers to the new universe en medias res, a few imaginary years into a largely "secret" continuity that would only gradually be revealed).
For the Superman books–mainly Action Comics, which re-re-re-re-retold Superman's origin, and Superman, set in the present–among the many big changes of the reboot was that of Superman's relationship with Lois Lane. Their marriage was dissolved, and, in fact, it never happened. These younger, less experienced versions of the characters weren't married, they weren't engaged, they weren't even dating, they didn't share in Superman's secret identity and there didn't even seem to be any chemistry, let alone romance, between the two.
As someone who is resistant to change in general, especially in comics where supposed fixes are often applied to things that aren't broken, I didn't really like the idea of Superman and Lois being de-married in a cosmic reboot. I liked them as full and equal partners, and thought their marriage actually contributed to making Superman distinct from so many of his super-peers (I also liked the fact that his parents were alive and he had a nice, healthy relationship with them; in The New 52, they were both dead).
There seemed to be two basic arguments for an unmarried Superman and Lois, however, one of which I find much more compelling than the other.
The first is the same that then-Editor-in-Chief Joe Quesada used in trying to justify the in-story reboot of Spider-Man Peter Parker and Mary Jane Watson's marriage in the pages of Amazing Spider-Man, that somehow having married characters limits the story options and ages them in the mind of the readers. I wasn't convinced, particularly since, at the time, Marvel had a younger, unmarried version of Spider-Man specifically designed to be distinct from the "real" Spider-Man in their long-running, actually rather great Ultimate Spider-Man.
But I could see where Quesada was coming from, sort of. Peter Parker was first introduced as a teenager, and original readers watched him attend high school and college and grow up over the issues and years. Even more so than most of the first generation of Marvel Comics characters, he was meant to be a character that was an awful lot like the young readers, who were only a radioactive spider-bite away from being a Spider-Man themselves.
Superman was never intended to be that sort of character. He was a more aspirational and inspirational character; the ways in which young readers could see themselves in him were a combination of wish fulfillment and metaphor. Superman was a grown-up whose stories were meant to be read by children; he was a dad-like figure from the start (The idea of superheroes a reader could relate to wouldn't really come along for a few decades after he smashed that green car and made that poor guy on the cover of Action Comics #1 grab the sides of his head in shock).
If marriage to Lois "aged" Superman, it did so only by a few years, maybe. And anyway, who cares? (Especially in the 21st century, when most Superman are adults themselves and, I'd guess, many of them are much, much older than Superman himself, whether he's meant to be 25, 30 or 39.)
The other, more compelling argument for un-marrying Superman and Lois is that it would restore the peculiar love triangle that was at the core of the very first Superman comics, the idea that Lois Lane loved Superman but despised Clark Kent, and that Clark/Superman loved Lois, but he wanted her to love him as Clark, not Superman.
That, and how the secret identity played into their complicated relationship, may not actually be fundamental to Superman comics (certainly plenty of stories of the modern age worked just fine after Lois discovered Clark's secret, and after they were married; and the argument could be made that doing away with the love triangle and the secret identity issue made the feature a lot less weird and its gender politics a lot less off-putting to a modern, audience composed of grown-ups), but they were certainly early elements, fuel for decades worth of stories in many different media, and, when The First Couple of Comics finally did tie the knot in 1996, there were certainly objections to the event, on the grounds that it was just too drastic a change (De-marrying Superman and Lois was a feature of the DC ixnay-ed "Superman 2000" proposal by Grant Morrison, Mark Waid, Mark Millar and Tom Peyer).
So I find it interesting that, now that we're looking at what could very well be the end of the New 52 continuity–the choice of the word "Rebirth" calls to mind Geoff Johns' Green Lantern: Rebirth and The Flash: Rebirth, both of which restored old status quos for those franchises through in-story events and minor retcons–that DC didn't really do anything with an unmarried Lois and Clark in the four years and change of the New 52.
Rather than restoring the Clark/Lois/Superman love triangle, the two were essentially platonic friends and occasional co-workers (Clark spent part of his career working at Daily Planet rival The Daily Star, and part of his career as a blogger). In the New 52, Lois Lane seems to have been Superman's Pal Lois Lane, his other best friend in the field, a sort of second, female Jimmy Olsen.
Wonder Woman fulfilled the role of love interest that Lois once played, as she and Superman were an item for just about three and a half years, first locking lips in August of 2012. If the New 52-iverse is coming to a close of sorts, than that would mean DC spent almost five years with an unmarried Superman, and the decision to decouple him from Lois had nothing to do with restoring what some might see as a core element of the character and concept, but instead so that he could date Wonder Woman.