"Random older markets in topics you follow" + add in "engaging", meaning, people who visit the market page have a high chance to bet.
This "engaging" concept and stat is VITAL. I want to see all engaging markets in tags I follow/bet in, people I follow. This will help filter out badly written or unclear markets, and will also make sure that markets which are fun to join get their needed exposure. I write a lot of markets with the purpose of letting people toss in 10m based on intuition and hope, then follow results. I'm trying to create useful, fun digestible content that makes you think! So I'd love if I could (find) and bet in more people's similar markets, and to have my own shared out that way too.
This is key to me. The popular image of prediction markets is that we bet on big issues like "will aliens be here by 2030" but if we don't surface those [existing] questions, they will never get bets.