If only SWF was extended to run deciders on AWS Lamda. Without this the main advantage of the Step Functions is hosting. I personally would rather see an integrated system where the Step Functions are a natural extension of SWF not a completely separate system.

This is the direction the Cadence is going. We are planning to add support for integrating custom DSLs easily, but maintaining the core code based libraries.

BTW: If anyone is interested on running the Step Functions DSL on top of Cadence contact the Cadence team. We could work together to get it implemented.