What a world assembly could look like

I identify some basic institutional features that can make a world assembly viable in terms of size and degree of complexity. The most potentially satisfactory model is a bicameral assembly formed by a lower chamber with about 2000 seats (of which about one-fourth would be elected in single-member districts and about three-fourths in multimember districts of proportional representation with moderate magnitude) and an upper chamber of territorial representation based on about 700 territorial units all across the world (basically corresponding to the nearly 200 currently independent states plus about 500 regional governments).