How would you like the feature to work? As well as being able to create a new theme from 'scratch' I would like to be able to duplicate a theme which could then be modified to create a new theme.
Why is this feature important to you? Having created a 'default' theme with various parameters defined (eg position & size of song text box). I would like to use this as a 'template' for other themes, usually just to change the background, without having to repeat my basic set up every time.