The "Rinoa is Ultimecia" theory makes FF8 way more interesting, shame it got officially debunked.
Though in Dissidia NT one of Rinoa's HP attacks is Apocalypse, which is only used by Ultimecia in FF8 so maybe their backtracking a little on that statement or just giving a nod to the theory.
On the other hand I hate the Squall is dead theory, like I understand it and see how it makes sense, but (and correct me if im wrong here) as far as I know it completely abandons everything the game built up to focus solely on Squall. What happens to the other characters? Does Edea just take over the world?