According the Schulz son, Marcie was modeled after a real person…a friend of the family. He was promoting a ‘Marcie movie’ which delves into her background and personality more completely called One-of-a-Kind, Marcie.
re: “smartphones and tablets, does that mean that they’ve always had them?” If they’ve always had them, then they presumably have a trove of other tech gadgets that we haven’t invented yet, and since I don’t see any of those in the picture, I guess it’s just a sight-gag on Wiley’s part.
Like inventing the human race, maybe… Or convincing Adam and Eve that they never want kids of their own…