This is cool, I wish the test data would change in the future because when we go to official WordPress themes repository, find a theme with a nice screenshot, then hit preview, all we see is the almost same preview. It's only show us different color schemes and typography.

That is not cool, right?

I think the test data being used right now is preventing user for seeing the potential use of a theme.

I just come to think that;
1). there should be some versions of test data to incorporate themes potential, like blogging test data, magazine test data, or portofolio test data. Developer can choose one version to be used when user wants to preview the theme.
2). or the option for developer to pick 'the right data' for their theme's preview. That mean the test data will be used partially on certain themes.

Just my thought though :)