There is a danger in "the more playable factions, the better." The more playable factions there are, the more testing and balancing will be required, and the more difficult it will be to get that "right." None of us want to play an unbalanced game. Hence, I think they should limit the number of playable clans to an amount they can effectively test and balance within the scheduled time allotted for the project. Within this limitation of scope, yes, I'd say the more the better.

I think it is important to acknowledge Oda Nobunaga and Toyotomi Hideyoshi as "unifiers" also. Most historians that I've read, do. The three are commonly referenced together as such because the outcome would not likely have been what it was had all three not done what they did. Tokugawa was the shrewd, patient, and fortunate one who took the final "prize," but it is not likely he could have done so without the accomplishments of his predecessors.