Section 126.96.36.199 of The MDL Programming Language describes the READ-TABLE (and similar PARSE-TABLE) feature, which a program could use to modify the parser at a low level, e.g. to add new punctuation.
MIM supported something similar but used a different table format. It was used by backquote.mud, among others.
If ZILF supported this, we could implement quasiquote syntax with a self-contained MDL package. We'd also have to implement <READ> so the handler could read the next object from the input stream and wrap it.