One really cool thing they could do would be to require tipping for every comment/submission vote. There was a site called witcoin in 2011 that did that, and it worked pretty well. But this would be such a major change that I doubt they'd actually do it.

Off-topic random thought: Someone should recreate witcoin. How it worked was that upvoting something had a small fixed cost. A large amount of this money would go to the submitter, but some of the money would also go to everyone who upvoted the post previously, with far more money going to people who had upvoted the submission earlier. This encouraged people to patrol new posts and only upvote things that are actually good. A very small percentage of the upvote fee also went to the site, though this was enough to make the site pretty profitable. It was a very fun site IMO. (It was shut down because of unrelated issues experienced by the operator, not due to lack of success/popularity.)