Making spam unprofitable would be a good first step. Rather than trying to detect whether something is spam or not, just target how spam sites are funded: ads,

Making spam unprofitable would be a good first step. Rather than trying to detect whether something is spam or not, just target how spam sites are funded: ads, analytics, affiliate links, etc and use those as a negative ranking signal. You'll still get spam if that's all that matches your query, but now all it takes is for someone to make a page matching the query without the aforementioned items to outrank the spam results. You wouldn't need to append "site:reddit.com" to your queries because the (mostly) non-commercial Reddit results would automatically outrank all the blogspam and listicles. If ads were downranked it would make a lot of spam/clickbait/listicles unprofitable overnight as they'd rank low enough that the costs of creating & maintaining the spam site/content would outgrow the returns from ad impressions.