[I wrote this comment on LW, copying to this post. Shouldn't that happen automatically?]
Nice post! I'll throw another signal boost for the Metaculus hackathon that OP links, since this is the first time Metaculus is sharing their whole 1M db of individual forecasts (not just the db of questions & resolutions which is already available). You have to apply to get access though. I'll link it again even though OP already did: https://metaculus.medium.com/announcing-metaculuss-million-predictions-hackathon-91c2dfa3f39There are nice cash prizes too.
As the OP writes, I think most the ideas here would be valid entries in the hackathon, though the emphasis is on forecast aggregation & methods for scoring individuals. I'm particularly interested in decay of predictions idea. I don't think we know how well predictions age, and what the right strategy for updating your predictions should be for long-running questions.