Meh, honestly I’m not so naive as to think anyone could design a system that couldn’t break or be broken, I think the best system is always “a new one” - dynasties always start fresh and die stale and so does any system, encrusted with cruft and iron triangles. That is to say, so long as the system has a feedback loop in which control is exerted through a mechanism (say, elections, or alternately the military support of lesser lords) that responds to policy.

If you’re going to maintain a republic you need a limited franchise of electors so self-sufficient that they’ll be fine no matter what, that’s been known for millennia.

I guess my ideal government would be one that changes forms randomly and unpredictably as determined by a meta-government. You could maybe even design an electoral system with three modes, in each of which a different leg of Arrow’s impossibility theorum collapses, so long as which mode to be used was determined by some Swiss functionary rolling a die.