After thinking about pogo pins a little longer, I decided that a card Edge Connectors option should be delevoped as well. They're durable, cheap, and easy to implement. The removal and insertion force for a card Edge Connectors, even with 40 pins, should be lower and less damage prone than with a 40 pin header connected directly to the Pi GPIO pins. Offering a card Edge adapter, as well as simple pin header connection on the carts would allow kids to handle the carts with less risk of damage to the GPIO pins(when using a card Edge connector), while allowing others to use the simpler and cheaper pin header. I dislike connecting anything to the GPIO header as the force required to insert and remove is fairly high and could cause damage to the system.

The simplest card Edge connector setup would be to just have the carts lay flat and plug the edge directly into the GPIO pins on the Pi 400. This would leave the cart sticking out of the back, and difficult to see when insterted. I'd prefer it to stand up right, so I could design a right angle edge connector adapter that would let the carts plug in vertically. There are benefits to both, and I will develop both and test. Vertical carts have the benefit of being visible at all times, which is handy for displays, speakers, and various switches. Horizontal carts have the advantage of not blocking the view of a display sitting on the same surface as the Pi 400, as well as being able to support things on top of them. Like coffee mugs and other hazards to electronics. A postal scale cart comes to mind here.

There are endless possibilities with this project and feature creep has to be managed to ever make any progress on it. I'll be buying some hardware and setting aside time to work on this soon. I have other large projects planned, but this one may end up being the most satisfying in the end.