If Moto could put it's two cents in.
I Will say that personally I enjoy playing two characters on the same island and especially when I was on Atamara "the island and I have a love hate relationship"
Having more than one noble in the same realm really does boost its strength but it could also kill a realm. Ex: if 4 players never talk but make up 8 nobles in a 10 noble realm ... That is one borring realm.
The new rule of one noble per island will cripple a lot of realm and many people in positions of power will not be happy. But I say go full steam ahead with it .