@robla that's a fair point, thank you for your response. In terms of the two-stage aspect in the US, I feel it is more of a de facto party-driven apparatus on top of the actual formal system, in contrast to France for instance where the two stages are the formally recognized method. You're probably also right that ranking more than a handful of candidates is generally pretty unpleasant. In any case I could be wrong about the difficulty of the sell, which would be good.
Approval top-two primary seems like it might be a decent option for single winner, although I figure it doesn't satisfy clone independence, which is pretty unfortunate.
For the fixed approval threshold, you're suggesting that if no candidate obtains the threshold, then the top two proceed?
"...under such a system, they might hire large analytics teams to ensure that both parties advance a sea of clones to drown out the other parties." Yes, exactly.
I was also thinking if there is a threshold, 50% should be imposed, since that guarantees some weak level of majoritarianism which seems important and that ordinary approval can lack.
In terms of single-winner, I'm on board with 50% approval threshold followed by a final round approval. I think that's really simple and seems to solve many problems.
In principle, it even could let people be lazy and not even bother with the second round if they decide that their first approval ballot is satisfactory enough for them.