Looks like an awesome concept, and well executed as well!

Since the GamePress arcade lets you play any GamePress game, you could even publish top games as standalone apps running on your engine (if the creator wants). But more interestingly, you could provide some "edit" functionality in these apps, so that players can modify their local versions using the GamePress editor (either the full or a simplified version).

Angry Birds is cool, being able to build Angry Birds is cooler, but being able to customize your own version of Angry Birds is the coolest. People love sharing things they make, so that could be an entirely new growth avenue.