[ST4] `#!/bin.sh`
This is not a valid she-bang
#!/bin.sh

and even if it is, its executable is not sh; but bin.sh
If it is invalid, just don't type it this way.
Highlighting is just lazy with what's allowed / prebended in front of SH.
I was expecting to use this as a visual reminder (I'd it's "not how it's supposed to be", it's wrong).
And laziness shouldn't trump "correctness"
The path may posssibly to point to anything there are propably too many variants to catch them all. Improvement suggestions are always welcome at https://github.com/sublimehq/Packages/pulls though.
And laziness shouldn't trump "correctness"
I disagree. That's what linters and language servers are for :)
I would consider anything starts with #! in the first line as an shebang, after reading https://en.wikipedia.org/wiki/Shebang_(Unix). The highlighting of sh in your case is wrong though.