Because there is not many themes built for Stepmania 4.0, I decided recently to make a new one. Its name is "DIAMOND", based on the default theme for metrics and have brand new graphics, sounds, animations and more...
There is no release date for the final product yet, but a fully-playable alpha version will be there for November.
Here is the website where you can find screenshots, videos and information about the theme and its progress.
I'll be pleased to read your feedback.