I recommend having at least in comment on the single-spa-examples.js making it explicit that the app code can live anywhere and that System.import will handle it. It just occurred to me that even though this is obvious, you will be dealing with people accessing that code with various skill levels.
Even though this project doesn't separate child apps into separate code repositories, that does not mean that it isn't possible. See https://github.com/CanopyTax/single-spa-examples/issues/7#issuecomment-262456119 where @mirandaleandro said