That's a neat trick; I don't think I've seen that before. It can be made to work for just about any language that has // comments.

It does rely on // which is implementation-defined according to POSIX. In some system //usr could refer to some kind of network path.

Last sentence here:

3.254 Pathname

A string that is used to identify a file. In the context of POSIX.1-2024, a pathname may be limited to {PATH_MAX} bytes, including the terminating null byte. It has optional beginning <slash> characters, followed by zero or more filenames separated by <slash> characters. A pathname can optionally contain one or more trailing <slash> characters. Multiple successive <slash> characters are considered to be the same as one <slash>, except it is implementation-defined whether the case of exactly two leading <slash> characters is treated specially.

[IEEE Std 1003.1, 2024 Edition]

It really is better for a language to either have # comments, or else support #! as a special case in a file that is presented for execution. You're also not launching an extra shell instance. (Too bad this // trick cannot use the "exec" shell command to replace the shell with the go program.)