Sometimes you need some business logic to be common to your native app and your responsive web UI (or server actions) but you really don't want two copies of it, one in a microflow and one in a nanoflow.
A picoflow would be a sub flow that can be called from either a microflow or a nanoflow. It would support most actions, but nothing that is platform specific.
The fact that we can copy and paste between microflows and nanoflows suggests to me that this would not be impossible to implement.