> The idea behind "not everything is an expression" is that ordinary macros only extend the expressions in a language.

That sounds great, for lisps, when everything is an expression. I feel like you haven't fully embraced lisp, because the article just kind of asserts that not everything is an expression, without justifying it.

In lisp the point of expressions isn't that everything has a return value, the bigger gain is that everything fits together, like legos. One of the big wins is that you can use your same toolkit, functions & macros, on everything. The point of the article seems to desire restricting that.