"with the requirement that the parameters always be in parens, that would be an error" : not really, because without parameters, you would have '() which is automatically translated to nil. You could do (fn (nil) nil), however, but I don't like the look of it. Not enough consistent, I guess (and a list containing the empty list to denote the empty list does not look right to me).
well, as a special form i don't think it would have trouble differentiating between () and nil. () seems to be different from '() even though (is () '()) is t
'() is (quote ()) while () is (). You won't notice the difference if you pass both to a normal function but you might if you passed both to a macro or special form.
While superficially (fn (. args) ...) may look decent, it is entirely inconsistent with the Arc reader. Function definitions have to be entirely representable in lists, and the example you list above is not a valid list. Not only would this break the current Arc, but you would have to reimplement the entire reader that Arc currently borrows from Scheme. Not to mention that you would have to define what it even means to have a cons with no 'car field.
