Ok, I plan to add a simple per-directory sort.. I hope that will be sufficient. (the contents of each directory will be sorted, but when shown as a simple list these may not appear sorted if they come from different subdirs in the artifacts tree).
Regarding zip download, it is always available.. ie, from a build page you can always tack /artifact on the end of the URL to reach the DirectoryBrowser which has the zip download option.. it's just that there is no visible link to this when there are < 40 artifacts.. might be useful to have such a link (but where? hm).