Great posts Brona. Only thing I might disagree with is whether this would have happened or not under Vito's reign. I think if he stayed out of prison then no chance it happens because he was simply untouchable at that point. Once he went away, it gave the Controni/Violi faction and Desjardins (who seemed to be plotting his revenge already) faction was ready to pounce at that point. They were biding their time and figured more than likely he would eventually go down and they got their chance once Massino started talking. Most like Di Maulo who knew that would sink Vito, probably let others like Desjardins who might have not known (I think he drove Di Maulo then so he probably did know already) that it was coming and they plotted their revenge once Vito started fighting extradition.
I just don't see anyone strong enough until then to attempt an overthrow of Vito.