Quicksand

After seeing the Trails & Tales Update, I'd say quicksand would be a cool addition to Minecraft. Quicksand would work in the same way as powdered snow, only with a different vignette effect. It will generate near / around desert temples and desert wells in large quantities, and randomly generated areas of quicksand can spawn throughout deserts. Also, if there is a medium - large area of sand directly next to a river, there is a chance some of it can turn into quicksand. The more you move and struggle in quicksand, the faster you'll sink, and eventually you'll begin to suffocate. I hope to see this as a feature in a future update.