I have the feeling that channels/coroutines is too low level

Channels are not really low level. Once you read the kotlinx.coroutines guide, you should be good to go. I use them a lot in my Android apps, and they just made their entrance to Kotlin/JS in 0.23.3

Compared to Rx is still low level, you don't have a clean way to abstract away the error path

@Jose Antonio Jimenez The clean way is having a class encapsulating the error or the value. Then, you can write an extension method to throw the exception or provide the value