By Evergreen Browser I assume you mean that the browser will have latest support for language syntax? That does not get rid of the problem of bundling though. And modern SPAs are so complex that bundling your own JS would be a nightmare. This is why NextJS is so great, they split the JS into SPA "pages" and let you dynamically load it from the server. I don't know how you could build that into native JS comfortably, since modules are smaller slices by far.