Today's update shows the level select screen coming together with more details. Plus, the beginnings of the progression system. 

I'm going to borrow the approach that Super Mario 3D World takes. In Too Many Sheep you'll earn Rosettes for all the herding you do, once you have enough you can unlock the town's sheepdog trial. Competing in that successfully will unlock the next town to explore. For the initial release of the game, I'm going to aim for 2 towns with 10 levels in each.