It's now been over two years since DC published a continuing Legion Of Super-Heroes title (not counting the recent Convergence tie-in, because, really now...Convergence.).
Back in the halcyon days of 1983, DC understood something fundamental about promoting the Legion Of Super-Heroes:
Don't worry about the "too large a cast of characters"--good gosh, the X-Men can remain popular despite that "handicap." How many Avengers are there these days? The large cast isn't a bug--it's a feature!
Don't worry about "too complex a back-story or continuity"--heavens, that's not stopping DC from running promoting Justice League 3000, is it? Besides, being set a thousand years in the future, if you've got a smart editorial team, you can pretty much ignore any events/continuity you want to. Dismiss it with a "records from that era were all lost!" aside...and just tell stories.
Teenagers with superpowers form a club to fight evil in the future--by Rao, what part of that is too difficult to grok?
From DC Sampler #1 (1983)