I am glad to get your input.
The specific duties that Tilapia might want to give its two provinces could be different than we currently do. In St. Esprit, where there is only one province in the country, this distinction is meaningless. Rather than thinking about the Australian model, perhaps the United Kingdom is more illustrative of our possible situation, with Scotland having different laws than England. I am not suggesting that we emulate the UK example, merely that we face some of the same problems, although clearly we are more divided now, and they had made certain steps relaxing centralization, and we are trying to discuss ideas to return an appropriate amount of centralization.
Each Autonomous State in CASE could decide to have a President, Monarch, or whatever as head of state. Each Autonomous State in CASE would have a head of government, which in the UPE is the same person as the head of state, but in Tilapia it is a different person.
The main point of this meeting is to figure out what powers the UPE is willing to give up to CASE or whatever the island-wide government is called, as well as what our neighbors would accept. We would have to give up some control to make it worthwhile for our neighbors to participate.
As to the rotation of the heads of state, this is done in many places, in the European Union, in Malaysia, where the "king" is chosen from among the sultans of the provinces, serves for a while and then another one is chosen.