The REST/Sinatra/MySQL solution was chosen in contrast to protocol buffers and Cassandra - the scaling potential of the systems are very different.
If you haven't worked on a project of this nature then the complications are likely not to be obvious to you. For instance, once this ships, they will be required to maintain that version of the REST API that was designed forever, including any side effects or semantic weirdness. If they determine that some changes are required for the sake of scale, they need to cross their fingers pretty hard that they can squeeze all of those changes into the existing API.
If this system were truly designed with Dianne's current abilities in mind, we don't know what that REST API looks like. Is it possible to imagine that it sends the full listing of recipes on every request? Absolutely. Are you going to be required to do that forever once the device ships? Yes.
If you haven't worked on a project of this nature then the complications are likely not to be obvious to you. For instance, once this ships, they will be required to maintain that version of the REST API that was designed forever, including any side effects or semantic weirdness. If they determine that some changes are required for the sake of scale, they need to cross their fingers pretty hard that they can squeeze all of those changes into the existing API.
If this system were truly designed with Dianne's current abilities in mind, we don't know what that REST API looks like. Is it possible to imagine that it sends the full listing of recipes on every request? Absolutely. Are you going to be required to do that forever once the device ships? Yes.