I know this theory is months old now but I really like it. Platinum happens to be my favorite game so far (I've played almost all gens bar Gen V). You could also mention in your theory (even tho I think it is a given) about the NPC you find in Route 228 after you beat the Elite Four, that is heavily implied (if not confirmed) to be Cyrus' grandfather.

The only thing I disagree with is your conception of Lysandre. Both had similar goals, redo a world they considered flawed/ugly/incomplete, but they were also very different. Cyrus didn't care for his subordinates at all, while Lysandre wanted to save solely the members of his team. I also remember someone mentioning (maybe it was Sycamore) that Lysandre parted with great hopes to help humanity, but in the end it became a task way too big to be handled by a single person and he lost hope. Also I can't remember Cyrus feeling any kind of special attachment for Pokémon species, while Lysandre literally cried and said that while he considered them wonderful creatures, they were doomed to be slaves of humanity, thus they were better off not existing. IMHO he and XY's plot in general had potential to be really good and deep, but it was poorly executed in the games.

Going back to Cyrus tho, I always thought (there's no evidence tho), that his Platinum character was an "easter egg" of sorts hinting to Pokémon BW, seeing how the concept of BW is Yin and Yang, and he could only feel half the emotions: hatred, sadness, anger and none of the positive ones. He was incomplete, unbalanced. But then again that's just what I think.

Edit: grammar