Sure, but where is that pure standard implemented?

Why does it need to be implemented somewhere?

What do you mean?

If the ISO SQL is not implemented by any SQL DB, and you denounce PostgreSQL/etc version of SQL - what is left over?

I’m not denouncing PostgreSQL. There’s things that are appropriate for a standard and other, sometimes far less elegant, things that are appropriate for a concrete implementation. The linked article propose a change to the standard. If it had only proposed a non-standard vendor extension for some or other database we wouldn’t be having this discussion.