I think 2 things about that:
The trending should be engagement based and not vote based
And the downvote system should be approved by a committee randomly picked by the blockchain from recently active accounts...
So it wouldn't be on hands of anyone specifically to be able to downvote
These are beautiful ideas but will surely come with their own issues.
Accounts with big stakes tend to have more engagements irrespective of what they post. You know everyone wants the attention of the whales. This means small accounts with fantastic content will have very little chance to make it to the top.
For the downvote committee, I sense there would be politics with selection which will become another problem on its own.
Still, engagement means people are interested while upvotes don't. Everything comes with a downside, we just gotta find the less down one XD
And with the votes, actually no politics would be involved if the accounts were just selected among recently actives ones that have not been selected in a time window...
But yeah, still would have the issue of people maybe not even knowing what is being asked from them.