What happens if your user is offline (airplane mode, no data, etc), and can't download the initial bootstrap script? There's no way to avoid an error page at this time, unless you use a browser-specific plugin (the drive offline addon is one of these, but they now use service workers for the same functionality on chrome IIRC).

This is especially useful in non-us, non-eu countries, where people pay a lot for data, relative to their income. Being able to successfully launch and run without any data usage is pretty rad.