Jojo's is already a work of comedy, but take what it already is and now imagine Joseph and Jotaro with thick cockney accents, Avdol as Bob Marley, Polnareff gains +6000% "HON HON BAGUETTE" style and Kakyoin is a drunk Australian half-assing his lines
Edit: in this hypothetical dub where every character is a caricature of themselves, Hol Horse remains entirely unchanged from original
Well, the English dubs of Parts 1 and 2 already use accents, so what they did isn't too far off from what we got. (Though, as someone who doesn't live in Europe, I have no idea how accurate the accents are. I imagine, like usual, they weren't very accurate.)