Having an open source application (aside from the sample application in the SDK) would be helpful for new third party developers.

While the sample application can be built, having an app like this available to "play" on the physical P3 might allow for some new devs to be able to see how certain actions can be completed within the framework more readily.

It's a very compelling idea.

I also think the app has a lot of promise for new and existing players to learn/practice some simple skills outside of the context of a traditional game (with goals that require said skills but are separate from those goals, if that makes sense).

That's also a great idea - since P3 games can now support every playfield module, it would likely be best to update with that approach in mind (which would also help with the educational aspect).