I would love to see iOS 11 bringing subtle touch down animations to standard system elements, such as navbar buttons, table view cells etc. By doing it to the default components, third party apps would be affected by it as well. This would make for a consistent and more compelling experience when touching iOS. And that sense of stiffness would be replaced with a much more fluid experience.
I like this idea. Apple Music's new play button has a great touch-down state – I wish more parts of iOS followed the same approach.