Skylum just released a free update for their excellent Luminar 2018 software that adds a Sky Enhancer Filter. The Filter uses AI to improve the sky in the photo and works pretty well in my experience.
Skylum have released a video demonstrating this filter in use
Lumina 2018 AI Sky Enhancer Examples
The examples below show an example of Luminar 2018 AI Sky Enhancer applied to a Fuji X-T2 Landscape of a Castle in Northumberland at dawn. The AI has done a good job of isolating the sky in the scene and the enhancements are natural. In this case dialled back to 60% worked better for the image.