Yeah...this could be set in the aftermath of DARKSEID WAR. Something HUGE goes down and the DCU we see in June is a flashforward, while JUSTICE LEAGUE catches up with the timeline...sorta how FOREVER EVIL shook out but in reverse, perhaps.
I see where you are coming from, but as most of the characters like Supes were Mid 20's anyway...it would bring Supes back to, what, 30-32 tops? The only thing that hurts my theory it means the teen characters like SUPERGIRL, Kon, the current Teen Titans would also be 19 or 20 years old and Damien would end up 16 or so...but then again there are ways to get around that (especially with Damien).
I also could see the advantages to this. With that device, it leaves a lot of wiggle room to slot in some stuff that didn't work before. For instance, a Kid Flash career (or perhaps even a brief FLASH career) for Nu Wally, so bam, some of the old Wally's history could be brought back into play in some form. Same with some elements of Wolfman New Teen Titans, Some of Superman's Post-Crisis history etc. Basically the restoration of the 10 year time span from the modern dawn of heroes to the ongoing stories. The New 52 era would basically then take place dead center of that span, with continuity and history to define on both sides of that line. Gives writers a larger canvas to work from when crafting stories while fixing one of the biggest problems with the New 52, I.E. the cramped time line. A win win I say.