a16z's Anish Acharya on why consumer AI is where the iPhone was in 2010, and the three reasons the biggest companies in the category haven't been built yet: "What's held us back is three things. One is that the models have been expensive, so if you want to do a free-to-use product, that hasn't been easy." "The second is that we've kind of had an interface problem. Chat makes sense if you're the highest agency person in the world, which is Elon and Sam. But for the average consumer, their…