I think it's pretty clear that they should have waited at least a few more months than they did, so they could at least get all their ducks in a row regarding consistent creative teams, some form of cohesive, behind-the-scenes Bible for the New 52 DC Universe (which character exist, which don't, what continuity was pitched, what was kept, etc) and at least a rudimentary continuity, so as not to have stories tripping over one another and writers retconning one another's work within the first year of this new supposedly streamlined and easier-to-follow new universe.
I've had three occasions in the last few months, however, to wonder if it might have served the publisher better to wait until now to do it, or at least within the last few months.
First, we have Grant Morrison's years-long Batman epic, currently un-folding in a second volume of Batman, Inc wrapping up, and while it's been pretty excellent (during all those years on the writing side; the art's been more up and down). Morrison's take was peculiar in that it assumed everything that ever happened in any Batman comic really "happened" in DC canon/continuity/history, even if in some somewhat altered form. It doesn't really mesh with the New 52's five-year timeline at all, nor do some of the core aspects of his mega-story (Batman conceiving a 10-year-old several years into his career as Batman, that son becoming Robin, a multi-national independent security force of vigilantes inspired by Batman working closely with Bruce Wayne, even little things like Robin Tim Drake becoming Red Robin).
It probably would have been better to reboot Batman continuity after Morrison's run ended, rather than a few years before, forcing bizarre alterations to the cast and some exceptionally goofy trade numbering. I'm pretty sure at least some of the other Bat-books could have been just fine if given another year or two before the reboot (For example, we still woulda had Scott Snyder-written Batman comics, they would have just kept appearing in Detective Comics instead of a rebooted new Batman series).
Second, we had Geoff Johns' run on Green Lantern ending recently, which occasioned the complete reshuffling of all of the Green Lantern creative teams. The same applies here; wouldn't it have been better to reboot Green Lantern continuity after Johns and company's run on the Green Lantern titles, allowing for a more pure reading experience of that epic and allowing DC editorial and the newer creative teams to have an actual clean break with Green Lantern continuity, being better able to pick and choose what aspects of Johns' run they wanted to include? (As is, Green Lantern continuity, like Batman continuity, apparently still "counts" everything, except for the many instances in which the events of the continuity must be different, leading to a worst-of-both-worlds kind of thing where new readers are still bombarded to references to older stories, but they can't consult older comics, because those events aren't accurate anymore either).
And thirdly, this week Scott Snyder and Jim Lee's Superman Unchained launched, which probably woulda made for a fine Superman #1 or Action Comics #1, particularly given the creative chaos that has engulfed both of those titles in the less-than-two years they've been around. As is, the book has become the de facto flagship of the five-book Superman line (six, if you wanna count Adventures of Superman along with Superman, Action Comics, Supergirl and Superboy).
It's a really tricky thing to try and armchair quarterbacck this far into the New 52—I'm not sure, for example, how the old DCU might have limped along for two more years with just the Batman and Green Lantern franchises kicking ass (Putting Geoff Johns on JLA immediately after Brightest Day in the old continuity and/or spinning he and Ivan Reis' Aquaman out of that tile woulda worked just fine though; I'm sure the JLI promised at the end of Justice League: Generation Lost woulda been just as well received as The New 52 Justice League International in the long run; and I would have loved to read two more years worth of Paul Cornell Superman stories after reading his "Black Ring" arc in Action Comics, as I'm sure plenty of others might have). And then there's the Jim Lee factor. He was a major selling point of the Justice League #1 that lead the New 52 reboot, and he's a major selling point of the new Superman Unchained book, and I doubt they coulda had him draw both arcs simultaneously.
Anyway, less than two years into The New 52, it seems like DC's got some really big, almost tectonic things shifting for them, and it seems a shame these shifts were taken into account when the decision to reboot the whole superhero line was made.