This is how I am approaching one of my app framework projects. HTTP is the delivery vehicle, but I only utilize a very small subset of the various full APIs (HTTP/HTML/JS/CSS) in order to deliver the framework's functionality. One of my objectives is for the framework to support a wider range of browsers than most modern websites are able to handle today. If vendors like Apple and Google begin fully-embracing things like PWA, I could wind up in a really good position regarding this approach.