I'd like improvements in basic usability. This includes filling in missing functionality (e.g. trig, socket connections, regular expressions) and/or an escape to Scheme to do these. Also non-brokenness on Linux, Windows, etc. Also ability to simply make a non-REPL Arc script. Picking up the Anarki stable fixes would probably cover most of this.
On the trivial side: w/bars must die.
One question: why is currying so popular? I don't see the point, so I guess I'm in blub-land with respect to currying.
The post by raymyers (http://www.arclanguage.org/item?id=3997) gives some very cool examples of the power of bracket-style currying. In addition to cutting down the number of tokens in the common [foo bar _] case of bracket-notation, it allows much nicer wrapping of variadic functions - or just functions for which you want to leave more than one argument open. Compare [* 2] to (fn args (apply * 2 args)), for instance.