I've been thinking about the Drago idea, though my thoughts kind of went away from son; I think a prized student and surrogate son may be thematically more powerful. Have Adonis face someone who idealizes Drago, even while being aware of who and what Drago was when he faced Apollo, without the myopic baggage of a blood feud and instead a more sincere "Yes, he is a flawed man, and yes he killed your father, but he's so much more than that, and if you keep calling him a killer, I'm going to defend him."
I think making Drago 2.0 be a reverse foil to Donnie rather than an exact one would be better. Donnie has issues regarding being an unintended illegitimate son that he's finally overcome, so have Drago 2.0 be more truly stoic and confident in his part of Drago's legacy to drive that home. Donnie is Creed's son but Rocky's student, so have Drago 2.0 be Drago's student but not his son. Maybe even do something with their styles; if Donnie is a kind of out-boxer/slugger hybrid, maybe have Drago 2.0 be a true swarmer, perhaps even an older and beaten one since he won't follow Drago's missteps.
I really think it might be cooler to have Donnie see an opponent he respects but from a school he loathes.
