Callback from a coroutine

I'm building a C# API for various network services. Currently my methods need to be polled to return data, but I'd like to upgrade this to have them trigger a developer-implemented callback.

I've established after some research that it is not safe to trigger a callback from a separate thread back into the main UnityEngine/MonoBehavior thread.

So my next thought - perhaps I can have my API take in the developer callback, start a coroutine but return immediately after, and eventually trigger the callback from the coroutine. I'm hoping to vet this idea before going too far down the rabbit hole, so I'll paste my proposed code below (somewhat pseudo) and if anyone has feedback as to whether or not this would be safe I'd greatly appreciate it.

Here is the example class that would contain the API:

 using UnityEngine;
 using System.Collections;
 
 public class DoAsynchronousStuff : MonoBehaviour
 {
     enum State {Pending, Complete};
     State state;
     
     // assume OutputData and InputData are classes defined elsewhere
     public delegate void Callback (OutputData data);
     
     public static void DoAThing(InputData data, Callback cb)
     {
         StartCoroutine(DoIt(data, cb));    
     }
     
     IEnumerator DoIt(InputData data, Callback callBack)
     {
         /* would be state machine here that hits a web service 
          * or something and updates state to Complete when a 
          * response is received (and populates an OutputData) */
         
         while (state != Complete)
             yield;
         
         callBack(outputData);
     }
 }

Then the developer implementation would look something like:

 using UnityEngine;
 using System.Collections;
 
 public class Sample : MonoBehaviour
 {
     OutputData outputData = null;
     InputData inputData;
     
     DoAsynchronousStuff.Callback myCallback = DidAThing;
     
     void DidAThing(OutputData data)
     {
         outputData = data; 
     }
     
     void Start()
     {
         // assume we've populated inputData already
         DoAsynchronousStuff.DoAThing(inputData, myCallback);
     }
     
     void Update()
     {
         if (outputData != null)
         {
             // do stuff with the data 
             
             outputData = null; // so we only do stuff with data once
         }
     }
 }