tbh there is very little reason why local storage is truly needed beyond perhaps cover caching and maybe background downloads of a series?
the trick is to first get the file size, search for the zip/rar file payload, parse out the image locations, then start downloading the file from that front, and as are images are exposed, render 'em! This isn't easy by any stretch but is solvable and would make comic zeal the killer app.
once that works, then it would be EQUALLY killer to have an ftp/sftp backend for actual comic content, using the app to arrange "logical" series, and the app maps back to the "physical" content of an ftp server -or- a local cache.
those two features would make cz THE killer app.
also,fwiw, cbz and cbr are HORRIBLE file formats because they really don't facilitate streaming. There isn't a reason to use a compressed package to store images, since most images are already compressed, and furthermore, there is no reason to store the package payload in the end, or in cbr case, randomly...it should be right there in the front, specifically SO content can easily be streamed.