Coincidentally, if you're thinking of adding pattern matching to the underlying calculus (not just as syntactic sugar), the book I mentioned in another comment

Coincidentally, if you're thinking of adding pattern matching to the underlying calculus (not just as syntactic sugar), the book I mentioned in another comment (Pattern Calculus) is worth a look. The author explores what a language could look like of patterns were first-class and used to express arbitrary computations. At the very least, it could be fun to have an extended version of the system (or a plugin of some sort, perhaps) using his ideas about pattern matching.