We can do this on some platforms, like the Scirra Arcade, or mobile (to the extent that you get an APK back for example). But for uploading to the web overall, it's hard to get a one-size-fits-all feature. Some people use FTP, others remote desktop, some by SSH, some use a special web interface provided by their host, etc. I don't think it's clear how we could feasibly cover all the possible cases.