We at JetBrains use it in production long before Kotlin 1.0 release 🙂
Our global license server, store and JetBrains Account portal use Exposed for more then 6 years.
About breaking changes. It happens from time to time to support requested feature like coroutines support but we are trying to make it as smooth as possible or prepare migration guides .
The closest breaking change can happen with release R2DBC support, but I hope it will require only to change imports in existing code.