@noelle @typhlosion @alice you have to see it in context: "build/do it yourself" kits and products have been around since ages, and they seem incredibly popular in japan, so people are willing to pay a bunch of money for that kind of thing there, see gakken kits and lotsa stuff
a lot of things nintendo does are pretty japan-centric, and this is just something they found marketable outside of japan
also, proprietary? it's cardboard, and the game coming with it is as proprietary as any other cart