I do not think that RAR files are necessary for J2O right now, compression may be better but it is not as standard or fast as a zip file. Now, the real problem with RAR files is that we would not be able to figure out the file contents like we currently do with zip files (a feature I put together and love ). While there is PHP RAR code it is not installed on the current server. RAR support will not happen without losing more important features like seeing contents of the zipped file.