[rntz]

Often you want the same code to expand differently depending on context, so I think it's still important to have explicit support for different syntax classes in a macro system.

Declarations are definitely a syntactically distinct class in, for example, Haskell or SML or C. Not so much in Lisp, Python, Javascript, and so forth.

I think the question of what an extensible extension mechanism would look like is a tough one, which is why I punted on it. I have worked on it a bit myself, as mentioned in another comment, but not in Lisp. I definitely might try my hand at a Lisp version in future, though, and I'm interested to see what other people might come up with!