But there is nothing stopping non homoiconic languages from adding first-class macros This is true, and Nemerle is an example of a language with this feature.

But there is nothing stopping non homoiconic languages from adding first-class macros This is true, and Nemerle is an example of a language with this feature. That said, it's harder to write macros in non-homoiconic languages. One can write Lisp macros by starting with the desired output and inserting quote and unquote where appropriate. Generating a syntax tree in other languages requires mentally translating them to something like Lisp.