The thing that would make this tricky is that a SensorDefinition needs to have an execution function, unlike a PipelineDefinition which just needs to express a DAG. So it's hard to get away from writing at least some actual code. (Similar to how you generally wouldn't create a solid from just YAML).
If you had a set of pre-existing sensor execution functions that you wanted to parameterize or configure dynamically into SensorDefinitions using YAML, that would be very doable though, using similar techniques to the PipelineDefinition case.