in PiW the `mx.data.action` is available but there is no right way of using it. It is not part of the API spec of the Pluggable widgets and is likely to be broken in the future.
For now it is not possible to get data directly back to the Pluggable widget, but work is in progress.
You can still use mx.data.action and use the return value in your callback. However, you need the guid of the input parameter and the microflow name as properties in your widget. This worked at least for string return values, I haven't tried this with objects as return value.