Are there any plans for b/create-basis when supplied with :aliases to combine any :extra-paths into :paths for you? I mean maybe not literally :paths but an appropriate key.

not sure I understand the question. those should get added to the classpath

are you looking for the "effective paths"?

if so, you can get that with a little bit of effort from the classpath map / classpath keys in the basis

(->> (b/create-basis
         {:user {:paths ["src"]
                 :aliases {:test {:extra-paths ["test"]}}}
          :aliases [:test]})
    :classpath
    (filter (fn [[p src]] (:path-key src)))
    (map key))
;;=> ("src/main/clojure" "src/main/resources" "src/test/clojure")

that's not necessarily correct ordering, but the ordering is defined in :classpath-roots key of the basis