Starting the discussion with the USAan model, there's an executive branch, a legislative branch, and a judicial branch. Do we want to have three similar branches? Any others? Do without any of the original three?
One constraint in the USAan system I'd like to see removed is the prohibition against holding an individual holding office personally responsible for hir actions. I'd like to see it mandatory, rather than prohibited.
Do we want two legislative houses? Assuming so, I'd like to have at least one be directly *appointed* by the people, as opposed to elected: People go and file a document appointing someone their representative, and if that person has, say, 10K appointments, they get a seat in the House, positively representing all the people who've authorized them. The more authorizations they have, the more powerful their vote in the House is. I'd also suggest the appointments as Rep be publicly posted on the federal website.