Additional level packs
As paid downloadable content
Emmanuel Mathis commented
I don't think tabs are good, there are already a lot of them, and users who just bought the full version will see additional paid content directly on the main screen, which isn't great.
I would rather put a button on the bottom of the overview page, which opens a list of available packs. Showing a simple image preview of one of the levels of each pack is enough I think, there isn't much differences between them.
Great idea! What's the best way to display them?
One page per level pack like the packs are now (with an unlock button at the top)?
All level packs on a single page (always last "stage") - like the current "overview" UI?
Entirely new UI screen?