That would be useful indeed. The flip side of the coin might be something that was sort of mentioned in 'on lisp'. If all functions return only one value (be it a list or a single value) by default, you can write a general memoize layer around functions that doesn't have to check how many multiple return values are returned.
I also noticed a carif function in arc. If you are worried about single values that will become lists in the future, you might start using carif in your current clients.
