It's a great feature, but GitHub's parser chokes on it.
Compare:
https://github.com/jchester/spc-kit/blob/eb2de71d815b0057e20...
To:
https://github.com/jchester/spc-kit/blob/main/sql/02-spc-int...
Basically the original rendering makes me look incompetent to a casual skimmer. Plus tools like JetBrains IDEs can suss out what comments belong to what DDL anyway.
"The web interface to the version control system doesn't parse the here-string correctly" isn't really a criticism of the PostgreSQL extension. It's a bug in the syntax highlighting.
The COMMENT feature isn't even a good choice for a VIEW, PROCEDURE, or FUNCTION, each of which already supports comments inline in the object definition on the server. No, the main benefits are adding comments to objects that DON'T retain them, like a TABLE, COLUMN, CONSTRAINT, ROLE, etc.