Thats all fine and well saying that he had planned a "Michael revenge" all along. But at the time of the meeting with the five families, there was no way for him to be sure that Michael would go back from Sicily and then propose to avenge his brother, like he told his father in the garden that while Vito gave his word, he didnt. There was the chance that it would go the way it did, but I really dont think you can say he had it all planned when he gave his word in the meeting with the five families.