So the entire reason why this is not a "real" shebang and instead takes the roundtrip through the shell is because the Go runtime would trip over the # character?

I think this points to some shortcomings of the shebang mechanism itself: That it expects the shebang line to be present and adhering a specific structure - but then passes the entire file with the line to the interpreter where the interpreter has to process (and hopefully ignore) the line again.

I know that situations where one piece of text is parsed by multiple different systems are intellectually interesting and give lots of opportunities for cleverness - but I think the straightforward solution would be to avoid such situations.

So maybe the linux devs should consider adding a new form for the shebang where the first line is just stripped before passing the file contents to the interpreter.