Agree,
1/ It could be run by witnesses. Just need a proposal to allow new content filters in witness consensus. (HF) Not easy though...
2/ It could be a solution like Hivemind or specific db like you mentioned with an open-source algorithm (and provably fair etc.) to query and sort the way we want.

I think your solutions, incl. the last one about not giving upvotes to people who use bid bots, are short-term solutions. Still, it can improve the overall quality of the Trending page, but we still need more long-term solution to keep aligned both interests:

• one with pay-for-visibility (incl. bid bots votes), because the blockchain allows it
• one with better quality content only with human votes (remove bid bots votes), to deliver the best content for readers...

unless we HF the Steem blockchain to remove the delegation feature, bid bots will exist because it's allowed and incentivized by design. So you have to deal with it and find a solution that doesn't necessary fight the existing reality. It can be just done by building an alternative that makes the current system obsolete: a New trending section sorting content by rewards without bid bot votes. If dTube would have it instead of the current trending, users would not be incentivized to use bid bots ;)

To be honest I don't think we will ever turn back on this Delegation model :(