I definitely think you can introduce new ideas with unschooling.
I only have a 14 month old, so you all are probably better qualified to answer this...
What happens to the motivation to learn? I personally think school is what kills it. I don't think it just magically ends around 1st or 2nd grade.
I've seen my daughter teach herself how to do so many things already and every day she works on mastering more. My only job has been to provide the materials she needs to practice and to model or briefly show her / tell her how to do or understand new things. (So, I do believe unschooling means acting as a guide, when needed. Parents are valid sources of knowledge, just like books and other sources are.)
DD takes it from there every time and works on things when she's ready. (She just came over and we had a little "lesson" in brushing mama's hair gently, in fact lol.)
Why would reading or math be any different? I've been a pretty trusting mother so far. My own mom is constantly horrified that I've allowed DD to feed herself and make messes and we baby-proofed to some extent and then let her roam and explore. I just follow DD's lead and let her practice the things I can tell she is itching to practice.
DD bumped her head a few times and fell down, pinched her fingers once or twice in a drawer, etc., but then quickly figured things out. I've never seen a 9 month old close a drawer so carefully.
I think learning the things she needs to learn to be successful in life will happen in much the same way. Reading, writing and math definitely aren't magical subjects that need to be taught in a class. They are skills that we use every single day in our culture.
