From the article, it sounds to me as though the webkitdirectory performance issue would only become a problem with excessively large trees of directories & file

From the article, it sounds to me as though the webkitdirectory performance issue would only become a problem with excessively large trees of directories & files. So, as you mention, in 99% (or more!) of cases it won't be a problem. Should they go with it, then? I don't know. Ultimately, I think, as you suggest, just getting something common to all major browsers that mostly works is more important than getting this absolutely perfect. Unfortunately, that doesn't seem to be what any of the browser vendors are aiming for.