Feels to me like we're about as close to that as we are close to regrowing limbs. We've made baby steps.

For one thing, the illustrated primer created content from scratch -- content especially suited to the reader. Mathigon and things like it can only present you with content pre-created by humans.

Secondly, the illustrated primer had an expert understanding of human development, human psychology, and human biology. It used this understanding, along with incredible sensor technology, dynamically to create complex pedagogical plans and follow them by presenting exactly the content the reader needs at the time. At the moment we have only extremely rudimentary planning capabilities (if any), extremely rudimentary sensor/input capabilities (basically limited to what to user types in), and extremely rudimentary algorithms capable of only low order logic (if the user does x they probably want why) with almost no understanding of human psychology.

Not to say we're not making great strides. We're just a really long way off.

Edit: thirdly, The illustrated primer had an expert understanding of every topic it taught Nell. I think we're a long way off from any computer system that has an expert understanding of anything. Our computers can do calculus a lot faster than we can, but they don't understand it at a higher order level.