In your examples, it's not the brackets signifying the multiplication. It's the adjacency that signifies the multiplication (as in e.g. 3x) and in they happen to need brackets to highlight the precendence which would be lost in e.g. 3x + 5.

The notation of the article logically follows because e.g. (4) = 4 but using that as a "cheat" to enable multiplication of numeric literals using adjacency is very rare I think.

No, it's not rare. It's still quite common when you have people manipulating literal numbers. The literal numbers are what's rare.

You say it's not rare, but I can't remember ever seeing it before reading this article.

Likely because you haven't encountered it since junior high school. It's not uncommon notation in pre-algebra and occasionally beginning algebra.

Yes, of course, I do know that. It's not what I meant.

Suppose we expand that first example. I would write: 3(x + 5) = 3x + 3⋅5 The notation I'm talking about writes: 3(x + 5) = 3x + 3(5)

It's that 3(5) instead of 3⋅5 I'm talking about.

I prefer to use a dot like you, but find calculations like "let x=5, then 3(1+x) = 3(1+5) = 3(6) = 18" acceptable, because each equation is just a lock substitution