B.R.I.L.L.I.A.N.T.!!!!!! I really hope that you are right.I've said before that this Watchmen business could have more to do with a character like Prime or Bat-Mite having read Watchmen and using it as a template to influence the DCU than the Watchmen characters themselves intervening.
That doesn't necessarily mean Watchmen characters couldn't appear but they might be constructs of Bat-Mite or something.
Keep in mind, if the darkness that infected DC was a "long time" before Flashpoint, it suggests a couple of things.
1. That Kal-L was onto something in Infinite Crisis when he suggested Hal's infection by Parallax, Aquaman's missing hand, Superman's loss of inspirational qualities, etc. was the result of a dark influence.
2. That Prime isn't the mastermind behind the darkness. His "retcon punches" created random changes, not deliberate ones. Although his time as the Time Trapper was, presumably, what happened to Superman's career as Superboy. He stole Superman's career as Superboy to create the Pocket Universe (ie. Crisis wasn't what caused it) and maybe to weaken Superman.
My wild conjecture is that Bat-Mite stopped playing with Batman for the most part around '86. He probably got really into DKR and Watchmen and started using his abilities to influence reality based on his favorite new comics he'd graduated to, thinking they were more mature but misunderstanding what makes them mature.
Oz, aka Prime, is a fanboy on the opposite (still bad) extreme who possibly became aware of Bat-Mite's tampering. He becomes Mr. Oz (because "we're not in Kansas anymore") and uses his own knowledge of Watchmen to try and oppose Bat-Mite's Watchmenification of the DCU. You could even see some hints of this in Jurgens' Bat-Mite book if you squint.
Bat-Mite tried to eliminate Superman in the New 52. But Oz countered by deploying a swiped Superman Red as the New 52 Superman.
The whole thing is a chess game between fanboys. And maybe at some point, Bat-Mite will conjure up the Watchmen characters (and DKR characters? and maybe Dr. Light?). Maybe Prime counters with Animal Man and the Inferior Five and Ambush Bug and so-on.
And the heroes will have to step in and say, "Look. We're not a happy comedy. But we're not paranoid and relentlessly grim." And basically have to defeat two mad gods, one Batman themed and one Superman themed.