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:as-alias doesn't do any of the circular dependency checks that the other ways of using :require do. So it would appear that circular dependencies are fine, however contrib tools like tools.namespace still do the circular dependecy even for :as-alias forms, and throw errors when they are encountered.
:as-alias doesn't load, so seems like circular dependencies are not an issue.
tools.namespace has not been updated to handle :as-alias yet. See https://clojure.atlassian.net/browse/TNS-56