By the client end do you mean on the Java or PHP side? I couldn't imagine it's that hard to do a quick check for a JSON/XML page on load, compare some strings, perhaps md5() some files for basic integrity checking and download updates from a HTTP connection for Java. I don't program Java, so I would be happy to be told it's not as easy as I think.
I'd be happy to make a PHP page that allows script makers to log in and upload new scripts, and then an api.php page which exports information about the version of the files that have been uploaded. Then the Java file could compare and offer the user an up or down-grade through a nice one-click screen on load.
I think it would transform and heavily increase the use of scripts, particularly the big support scripts, I'm thinking universal_recovery, newLife, etc. as well as the frequently updated turn-burners, my ascension script, the nemesis and basement ones, etc.
Java. I think the vision is that the functionality is embedded into KoLmafia although using it would presumably be a manual or an opt in automatic process. See comments above about reinventing the wheel as well as trusting files and URLs that are the source of downloads.
I'm interested in your comment about increasing script usage. Presumably a new ScriptManager tab or window in KoLmafia might trigger the interest of someone who doesn't know about or never visits kolmafia.us but I don't hear people complaining about the process of finding scripts, determining which ones to trust or keeping them updated.