Was going to construct a long response for the Gnome Games list about how games can encourage types of learning and development and also how much OLPC would love that kind of thing.

Might even work out nicely for you if you plan from the start to write an engine and make the rest of the project seperate work that others can be encourage to do.
This kind of works for Aisleriot.

Not enough time for a more considered reply but I wish you the best of luck with your project and I guess I’ll volunteer as a tester etc.

@Michael
compare and contrast Frozen Bubble and Monkey Bubble. Gnome might not be ideal for game writing but it is certainly a possibility (and thanks to Cairo the canvas might still end up getting the benefits of an OpenGL backend depending on how things are done).