Currently, there are game modes based on national boundaries (country streak, battle royale countries) and US state boundaries (state streak). My proposal is, allow users to create their own boundaries for custom streak or battle royale games. For example, one user might draw the prefectural boundaries of Japan, another might draw the boundaries of world trade blocs. I've already published some boundary-related maps (boundaries between language families, between continents, etc). There's another open feature request for a map based on ecosystem boundaries. Those are all examples of things we could do with this proposed feature.