I'd like to see that as well, the biggest issue with Arabic is that in order to learn the language, the script must first be learned, and it's one that's very, very different from Latin. The learning curve would be huge, even moreso for the script than for the language itself.
Yes, please add Arabic! LiveMocha's Arabic is dreadful right now because there is no introduction to the script or way to learn it and the recordings are poor quality. I love DuoLingo for Portuguese and Spanish, so hope Arabic comes soon!