This is somewhat similar, but I've taken out the part of the embedded teensy because I wanted to keep the cartridge in traditional format. I changed the circuit somewhat so the memory can be flashed later on from the cartridge connector.
I'll have to see how many people will buy a cart like this and will check later on if it's worth it to design and build a programmer connector for it. A programmer expansion would also require good software to go with, all and all a task at itself. I decided to phase it out...