Well, this sounds like a good idea but i think there will be again some problems with simple yes or no. Let us assume that 65 % said yes and rest said no. Then, again large chunk of voice will go unheard and sooner or later there will be some problem. Again in the 35 % also you will have people who want complete monarchy, constitutional monarchy and ceremonial monarch. Though addressing all people's demands voice may be near to  impossible but at least the decision needs to be acceptable to all the sections of the society. IMO, it is in this scenario that the constituent assembly can play a major role. However, with the present  political leaders I think the constituent assembly looks a distant away and even if it is held we all know the capability of the present day leaders.