Leading questions:
Representative vs Direct Democracy?
Unitary or Federal?
Presidential or Parliamentary?
How much separations of powers should there be? In presidential systems, such as the United States of America, there is often deadlock between the executive and legislature. In parliamentary systems, the head of government is elected by legislature, therefore, there is practically no deadlock as long as theres is majority support of the executive in the legislature (although, there can still be courts to determine constitutionality of policiss). Would you prefer more checks and balances, but can also result in more deadlock, or a government more easily able to enact policies, for better or for worse?
Electoral method? FPTP? Two-Round? Ranked-Choice/Single-Transferable Vote? What about legislature? Should there be local districts? Single or Multi member districts? Proportional-representation based on votes for a party? If so, how should the party-lists be determined?
Should anti-democratic parties be banned? Or should all parties be allowed to compete in elections, regardless of ideology? In Germany, they practice what's called "Defensive Democracy" which bans any political parties (and their successors) that are anti-democratic. Some of banned political parties include the nazi party.
How easy or difficult should the constitution br allowed to be changed? Majority support or some type of supermajority support?
Should we really elect officials, or randomly select them via sortition?
These are just some topics to think about, you don't have to answer all of them.
Edit: Clarified some things
How would be such a debate of ten milliards of people moderated? Who would decide, that today, we shall vote about the water, and tomorrow, about some boring technical norms of street lights? If you have an answer, how would be this solution resistant to a misuse?
Would we haveanything like a constitution? And how would be principles of subsidarity achieved?
These are some great questions that I don't necessarily know the answer to.
I imagine a discussion platform kind of like Reddit / Lemmy, but where moderators are all democratically elected. This would ensure that the community always has the power to remove moderators that aren't serving the interests of the community. In terms of how changes are made, I imagine an environment that combines the best features of Github and Wikipedia, in terms of how changes are made and decided upon and applied for everyone. That there would be standard processes in place for making suggestions and changes, but that the ultimate power rests in the hands of the community participants.