I developed a hybrid mobile app using webpack/react/rxjs/cordova, so I have some experience with the ecosystem.

Unless you are entirely using third party services, your single page application is probably contacting at least one service you also have to write. Now you have 2 applications to worry about, not just one. It adds complexity to your development, build, and release process. That complexity might be worth it.

Hmm. I found it was always worth having a clean separation between frontend and business logic, so I would have built at least two modules anyway. I feel like if you want to smush together the frontend and backend pieces you can do that with node - they're both just javascript files in different folders, you only have one build process, and you just run "gulp run" or whatever during development - but I've only done that on one project so maybe I'm misremembering.