This is kind of a no brainer but Blender currently only shows the ETA for each frame only when rendering animations. I know that not all frames won’t render at the same speed depending on the complexity of each frame. It would be the best if Blender measures the average render time for each frame and then simply shows the user how much he has to wait approximately. Or maybe take the fastest frame render so far and the longest frame render so far to display best case and worst case ETA’s for animation render.