Support a .buble config file
Currently config variables have to be given on the command line or as an object when using Bublé with the JS API.
The problem is that this means that 3rd party projects like buble-loader also need to support a way to pass through these options. See for example this issue on buble-loader.
Now if Bublé would support a .buble config file, then buble-loader wouldn't have to add support for passing in options.
Another positive thing is that if you use Bublé from the command line, that you don't always have to pass in the same options over and over again, they are nicely located in a config file, committed to source control.