I think NBI are holding the biggest bitcoin so far, coz what happened to Mt. GOX Although 200,000 bitcoins have since been "found", the reasons for the disappearancetheft, fraud, mismanagement, or a combination of thesewere initially unclear
I do suspect the same thing too which NBI do hold up large amounts of bitcoin as of now and for sure they are keeping it and dont expose into public into those holdings since that amounts is already huge considering on the price of a whole bitcoin as of now.I dont even think that satoshi holds up large amount but who knows? and even on second one no one really knows who holds them and whose the one who posses it because of anonymity of bitcoin these kind of questions would really remain unanswered.