Yes, that's true, Danito. But I don't think Michael intended Vincent to be his successor, literally. Vincent would be more like Zasa's successor. I've said before that, if Michael'd had his way, he'd be "completely" legit (by his definition), running Immobiliare with his usual ruthlessness. A guess is that he'd use it at least in part as a money-laundering vehicle (why else would he be interested in an Italian real estate firm?). Vincent would be head of an ever-shrinking "olive oil business." having gotten that "prize" by giving up Mary so Michael could arrange her marriage to a "legitimate" husband. Vincent would be lurking in the background as an ally and a warning of violence to anyone who opposed Michael in the "legitimate" world. He would be to Michael as The Ant was to Zasa--but at arms-length.
dt, I agree with you that Vincent's rise was too fast to be credible. It's one of the many plot flaws that diminish GFIII.