Been advocating this for awhile as a thing that'd be good even if I don't find it likely; here's my arguments:
* He’s been the Time Trapper, so he’s acquainted both with cosmic alterations and rocking the evil robe look.
* His whole deal since becoming a villain has been “The DCU must be like this, and I will eviscerate anything between points A and B”. This would just be pivoting from the Silver Age to the Dark Age, explaining for instance how and why Vertigo and Wildstorm got integrated into the main universe - if he got
way into 80s and 90s comics for all the wrong reasons, of course he’d think they should be in there.
* He vanished from Earth-Prime in 1985. The first major comic after that for him to read when he got back would have been Watchmen.
* Oz’s symbol is literally ‘nostalgia’.
* His one direct victim so far is Tim Drake, who he’d hate both from before as part of the 90s, and now for being too bright and silly. Flashpoint also specifically screwed over the Flash Family, who he has a grudge against (especially Bart Allen, who got off the worst by being turned evil), and Kon-El/Superboy, his ‘nemesis’.
* His defining visual aesthetic is to wear a doofy armor version of the Superman costume.
* And given they’re already into visually homaging Watchmen, well, there’s something pretty obvious right there:
So yeah, Superboy Prime finally makes it home and discovers Watchmen and the 90s happened, gets super into it, and decides DC needs to be that now, smashing it together with everything complicated and harsh and depressing and dumb he can force in, now trying as his endgame to just plain make Watchmen a part of that world. Everything dumb about the New 52 would magically be transmogrified into genius, because the understanding is that it’s because there’s a dumb fanboy behind the wheel. And it would partially redeem the very concept of DC Rebirth, since it would turn out Johns & company were spiritually admitting their culpability in what DC’s become instead of just pointing the finger at Moore. Which would of course be the main reason this definitely won’t happen, but I feel safe in saying this would work better than him turning out to be Ozymandias or whatever. Plus Mr. Oz constantly enigmatically muttering to himself like an idiot’s idea of a mysterious mastermind figure would go from “oh my god, this is how Dan Jurgens thinks Ozymandias speaks? Jesus Christ, this is just painful” to
hilarious, because now you’d know that after every vague dramatic declaration, he’d be thinking to himself “yes, nailed it, I sounded like such a badass, they’ll never guess your sweet plan Clark, you’re so much cooler than these losers”.