Well, essentially we already have 'avg:list as the variadic version. In fact, it looks like we can shave off two characters:
(map(fn e avg.e)r t)
(map avg:list r t)
I don't remember ever using 'avg except maybe to average some time measurements at the REPL, and I think the idiom (avg:accum ...) comes in handy for that. But I generally don't use arithmetic operators in my programs, probably due to the subject matter I choose.
After I wrote that comment it seemed to me that variadic is more fundamental, because you can always convert lists using apply. But you're right that it's not hard to bounce between the two.
