How come there aren't any mainstream mint-flavored sodas? A syrop de menthe with fizzy water is delicious and refreshing in the summer, but you can't buy anything like it pre-mixed.
A co-worker suggested that it's because people would think it tasted like mouthwash, but I think you could come up with versions that didn't. Especially if you added some lime and sold it as a mojito soda.
Get on that, soda companies.