Really like the idea for the card template.
Have you considered using a cutting machine such as the Craft Robo
eg here http://www.graphteccorp.com/craftrobo/
Many primary schools have these machines, so making a template for a Raspberry Pi box could fit well in the primary curriculum. There is also a lot of potential for art work here too.
I worked for several years on the Techlink project where secondary schools assist primary schools with CADCAM Here is an example of a video demonstrating part of a racing car project for primary schools.
I believe integrating computing, programming, CAD/CAM, and design, in primary schools would be popular. Allows children to work together on different disciplines and develop their teamwork.
We developed these ideas working with the Nuffield Foundation and produced some teaching materials for primary schools http://www.techlinkinschools.com/?cat=18
Maybe there is potential here for a Nuffield Raspberry Pi Case project.
Possibility of sponsorship for schools needing resources, if there was interest in this.