Where does continuity end? How removed can a series be from the rest of the setting and still be called part of it? The is just one of the many problems The Legion of Super-Heroes introduces into the Drewniverse. While they are removed by a thousand years of future history, the Legion also creates continuity problems, working against world-shaking reveals and the like. I mean, if you have a club of kids in the 31st century dedicated to the hero worship of early 21st century heroes, they'd know all about the Big Events of the past. Given that we're writing this reboot knowing that everything will come around again in 10-15 years or so, that means that the Legion becomes a defacto spoiler.
The Entities that coil about the center of the Lantern Conspiracy will not devour the universe - we know this because the Legion exists. Superman will not give up on his humanity and run mad with dictatorial power - the Legion still praises him. Darkseid will not destroy the Earth, Atlantis will not rise from the waves, and Brainiac will not put the moon in a bottle. To push the Legion farther away from being spoilers - creating Time Barriers or Bubbles or Amnesia Rays or whatever, just further removes them from the continuity. At that point, they just become generic Teens Innnn Spppaacceee.
I'm loathe to do that to the Legion. Not because I have any love for them - I should be honest that I don't really care for them - but because historically, creating a hero or group that operates without interaction or awareness of other heroes or groups is what causes continuity screw-ups that end up necessitating re-reboots. Remember Superman and Batman were born in isolation and operated for years without acknowledging that their worlds were the same. Binding them to the same continuity created some "It's best if you don't think about it too hard" headaches that remain to this day - the locations of Metropolis and Gotham City, for example.
That said, I've already acknowledged that the Legion exists in the Drewnieverse. As a young lad, Superman had several adventures with the Legion, called to the future by their Temporal Zeta Beam. These adventures would be covered in short arcs in Action Comics, the anthology Superman title. The Legion encountered here would be the "classic" Legion - Cosmic Boy, Saturn Girl, Lightning Lad, and so on. Every so often, they'd call up Clark and have him zip forward into the future in order to help save a planet that's slipped its orbit or stop a galactic dictator or something. "We can't tell you everything, Superboy," Cosmic Boy would say, "Because we don't want you accidentally changing our past. But we know you're going to need the experiences you get here sometime in your future, so let's get to work!"
Very positive, very bright, very fake.
The Legion of Super-Heroes in its "teens changing the universe" guise is for the most part a lie. I remember reading about search and rescue dogs used to locate survivors following a disaster. If the dogs could not locate a survivor by the end of the day, one of the dog's handlers would hide him or herself in the rubble and let the dog search them out. Apparently, they had to do that because otherwise the dogs would get depressed or stressed at their failure. That's the role of the Legion in the Drewniverse - they exist to provide comfort to our heroes, lest they get subsumed in the Grim Grimdarkness of their daily grind. The comfort our heroes by showing them a future world where yes, challenges still exist, but they are extremely black and white ones and can be overcome through positive thinking and stick-to-itiveness. The 'future' that Superboy is brought to is not the Legion's own - it's one of the many possible futures that exist. The Legion would hand-pick one of these futures on the cusp of crisis, pull Superboy into it, and go about saving things.
As Superboy grows into Superman, the Legion keeps at it, bringing him forward into a possible future where he can confront and defeat a foe cleanly. It's almost like a heroic vacation, a chance to use your powers for good intentions without paving the way to hell. In the real world, Superman must feel like he can't save a cat from a tree without worrying about if that's the best use of his time. Sure, it only took 15 seconds, but that 15 seconds could have been used studying human DNA to locate genetic markers for cancer or something. Legion victories are complete victories. When he's too busy to head off into the future, Superman refers some of his Justice League pals.
So in Legion of Super-Heroes (#40/52), we'll be pulling back the curtain surrounding Legion activities. We will follow the story of those Legionnaires who work (mostly together) to set up opportunities for the heroes of today to not only train, but reinforce their own moral decision that what they are doing with their powers is right. The Legionnaires act as peers to developing heroes, often interceding early in the hero's development ("Green Arrow! The future needs you! Come with us!") and subtly teaching them moral and ethical lessons before returning them to their time (complete with a warning to not discuss their adventures in the future for fear of altering the Legion's past).
Basically, the Legion of Super-Heroes in the Drewniverse will fill the same role as the JSA does in pre-reboot DC.
While the Cosmic-Saturn-Lightning trio make for good facemen, the actual leader of the Legion will be someone smart enough to deal with the logistics of time travel and alternate futures with some prior experience in setting up bottle realities - Brainiac 5. He/it will be the true nucleus of the Legion, tasked with its creation and maintenance from birth. Everyone else is someone who has been recruited into the Legion, selected from thousands of variations of themselves to fill some role B5 found lacking. The rest of the Legion is not aware how thoroughly Brainiac has planned things - heck some of the recent recruits are in the dark as much as the heroes they pull up from the past. Even those "in the know" think they are pulling one over on the heroes of yesteryear in order to inspire and train them, not aware that they themselves have had one pulled over on them.
This setup will hopefully give the Legion an active role in the 'modern' Drewniverse, allow for them to interact with the rest of the cast of heroes but in a setting limited enough that they won't be in a position to spoil future events. Plus, it gives a training element to the setting, one that we're missing now that time's implacable march has stolen the JSA from us. Then there is the mystery of the Legion's true goals and Brainiac 5's motivations, something that will unfurl over the course of the comic. Revelations, such as Brainiac 5's creator (an alternate future Superman who took over the galaxy), would come as counterpoints to revelations that occur in the main setting.
Legion of Super-Heroes will not be the only Legion comic in the Drewniverse, but it will be the only one in the starting 52. The later comic, Legion, would require a bit more motion to the setting, seeing as it would be based on both the 'training' premise and a callback to that other Legion that exists in the DC Universe...