One of my fears about doing this at the CDN level is that now introducing a new syntax feature means you need the browser to support it AND the version of the Binary AST compiler on your CDN. Imagine using a new JS keyword and all of a sudden all your code gets slower because its a syntax error at the CDN level. It would just slower the rate of introduction of new syntax features I think by needing a lot more coordination: its already a bit messy with different browsers having different support, now caniuse.com may need to include CDN's too.