Hi,
I'm really disappointed to see the Render Selected option not helping reduce the rendering times as much as it can. Let me clarify what I mean and discuss what can be done:
I needed to change the texture of a small box object in one of my scenes, and I've had the chance to use selection render for the first time.
Whole frame rendering of 500 frames animation would last about 5.5 hours.
Selection mode with single object selection reported 3 hours 25 minutes, which according to my experience with other renderers, I found unnecessarily long.
I've set a region along with Selected option and now the predicted time is 1 hour 25 minutes.
The predictions are solid.
It seems a feature to set a border region around selected object's extents and render only that region would help reduce rendering times drastically.
This reduced the rendering time to almost a half.
In my case, as the camera was moving, I've set the region extents to cover the object's extents throughout the entire animation so this is even less efficient than what you can implement as a feature.
Feature Name : Auto Region Selected :D - or just go on with the Selected but set a region. ı guess it will work.