Right. But since this is a group about the ISO/ANSI standard, those product-specific things are irrelevant for answers with respect to what is or is not covered in ISO/ANSI SQL.

That's a strong statement. I don't know which requirements a certain application may have to need such a feature. So I would never be in a position to claim that it "never makes sense". But that's beside the point. The point is that grouping the result rows is an orthogonal concept to the SELECT list. The only dependency that exists is that aggregate functions are applied to a group defined by a GROUP BY clause. For everything else, there are no strings attached. That's what the standard requires and what products implement.