Since they have BY FAR the most stake, they could downvote the worst offenders. A 1% downvote from the @steemit account would have the weight of a little over $7. They could hire an intern to sweep away the garbage from trending once a day.

Currently not only is there no danger from abusing the system in this way, it's PROFITABLE in most cases.

They could also just completely dump their current trending page and instead use posts voted on from curation guilds. This would be a band-aid and not a solution, but it would be better than the current situation. It's what Steempeak.com does, but it would be a lot more powerful and beneficial to the blockchain and their bottom line to do it here since this is where all the traffic is. This would also make bidbots as a form of promoting posts less attractive and help with that situation.

They could fix their built in post promotion feature, by having promoted posts show up on trending(assuming they didn't do the last idea) This of course wouldn't be able to compete with Bidbots, but again they could just ban bidbots, by using their stake to flag posts that reach the top of trending through those means. They don't need to track down every single plagiarist, just make sure it's not on the front page.