i've seen a lot of people say this but anyone thinking like this is really forgetting a universal truth about joestars which is that they're all good at heart and are known to have strong moral compasses. therefore by joestar nature i don't think jodio would turn on what's seen as the good side. i think jodio carrying the joestar last name really emphasizes this despite his dio like behaviour.

i personally don't see much of a chance of jodio becoming the villain purely because of the nature of how the franchise has structured its storytelling for each character to overcome some internal and/or external conflicts (jodio's likely being his struggle to understand his own feelings).