I should add that I'm seriously considering getting rid of SWITCH/DEFAULT. With void as the generic signal for "this action was a no-op", there's a much richer landscape of ways to deal with defaulting that apply to every operation that obeys the conventions.
More useful IMO would be to add SWITCH/ALL. With the ability to do soft-quoted evaluations, there are actually meaningful use cases for switch/all x [...] also [...] else [...]
This would be a change to the core C native--obviously a SWITCH which supported /DEFAULT could be grafted on top of that.
Update June 2018: SWITCH/DEFAULT eliminated
Update September 2019: /DEFAULT can be added back to a derivation of SWITCH for compatibility via AUGMENT