The extension I used for Just syntax highlighting prior to this one, https://github.com/sclu1034/vscode-just, had support for syntax highlighting of shebang lines: https://github.com/sclu1034/vscode-just/blob/06bd5616532470280946c45fd29e5784069a23b2/syntaxes/just.tmLanguage.json. I would love to see that with this one as well!