Great start. One thing that should be added (whether to this toolkit or to someone else who makes one) is a way to tie different variables together. For instance, the ability to make a slider to increase the run speed and trail length together, or landing squash and gravity together.
Here is a good article on this idea, in more general software tools.
I agree that these would make the toy/tool a lot better, but it does seem like he built a game engine that starts you off with a game. If that's right, then it would take a while to implement much of these.
This might be a faster way to get there: if there was a way to bridge Platformer Toolkit to Unity and show the underlying code, it would let us reverse engineer his process and add more useful features in a shorter amount of time.
