Happy New year @dan! My opinion is to have:

• reputation separate from SP and it should be harder to gain and easier to loose?

• Have random upvote periods (encrypted for 7 days) so that it's harder to coordinate attacks.

• Proof-of-human® is also essential but how to do it? Sign/Hash/Encrypt all your fingersprints and ask randomly for one of those prints? A couple of modern phones have digital fingerprint readers...