Good question, but ns.arc manipulates what Racket calls namespaces, which are data structures that carry certain state and variable bindings we might usually think of as "global," particularly the definitions of top-level variables.
What Common Lisp and Clojure call namespaces are like prefixes that get prepended to every symbol in a file, changing them from unqualified names into qualified names.
I think namespaces are a fine approach for Arc. If Anarki's going to have both, it's probably best to rename Anarki's interactions with Racket namespaces (like in ns.arc) so they're called "environments" or something, to reduce confusion. I think they will essentially fit the role of what Common Lisp calls environments.
Of course, people doing Racket interop will still need to know they're called namespaces on the Racket side. Is there another name we can use for Common Lisp style namespaces? "Qualifications" seems like it could work.