My largest criticism for projects like this is that I absolutely abhor running into compiler errors. When you don't fully trust the compiler, it suddenly become

My largest criticism for projects like this is that I absolutely abhor running into compiler errors. When you don't fully trust the compiler, it suddenly becomes a suspect when code isn't working like you think it should. Given decent source maps to allow debugging through the original code, I don't think solutions like this are terribly different than native Javascript. The primary difference though is that I trust the browser JS interpreters and VMs more than I trust many X->JS compilers.