It's really simple. Rebirth writers are taking liberties as to what a LOT of characters have been up to recently. From villains totally changing their status quo (ie the Rogues, even though they just did that to **** with Flash) to whole teams just kind of dissolving and new ones forming.
So I don't think it's too hard to imagine a scenario where Harvest, on a secret search for a new technology in his bid for metahuman control, bites off more than he can chew and is left in hiding barely clinging to life and his few Ravagers that remain and his last remaining "prize" Superboy (Kon El) in stasis.

Now heres how we get our old Kon back without dismantling what happened in the New 52. Everyone's remembers the memories that were given back to the aged Titans when the pre-flashpoint Wally West touched them right? Well say that Harvest catches wind of a young new Flash working with the old/new Titans ? Makes a commotion to lure the team there in an effort to control them and kick-start his operation back to life. It would obviously backfire and the team would find Kon El in stasis. Wally, recognizing Superboy from his past life goes to free him and upon touching him (like his teammates) sends a flood of pre-flashpoint memories into him, giving Kon a new perspective about himself which lets him act more like the Kon we love. It could also override Harvests control on him and leave him free.
I think he'd make a wonderful addition to the new Titans.

Just my idea I think it's pretty cut and dry , and easily done. I don't even think it'd require a 4 issue arc. Maybe two.

What do you guys think?