Hello,
I know it is spelled out in the documentation that premarket and after hours trading are not supported in the API. This feature would allow developers with full time jobs doing something else to spend time testing before and/or after their main jobs are complete. Without this, they are stuck testing mid-day or when the markets normal hours are open.
Implementing this feature would likely increase the usage of your API by more developers as it would allow them to complete code quicker.