YAML is definitely the hotness right now but it works. No need to invent a full blown language for something like this. Way easier than trying to write json.
Giant disclaimer: I work at StackStorm...but I also have an extensive Ops background.
This is really the next step in runbook automation. It gives users a way to express procedures and operational patterns in code (the workflow definitions are in yaml). With any sort of automated remediation there is always the concern of "painting over the mold" but at the same time you don't want to get stuck doing a large number of manual steps when you could be focusing your energy on tracking down the root cause of the issue and resolving that. The more important aspect to me personally is the easy of version controlling these ops patterns. Store the workflow definitions in source control and it is easy to diff the changes in your procedure.