It would be great if in addition to being able to access folders, web apps could also save folders. This would eliminate the need for folders to be zipped, downloaded, and unzipped, which is particularly ridiculous when the folder is stored someplace like a local sandboxed file system. It would also be consistent with user expectations, as things like Google Drive allow folders to be uploaded but downloads are zipped.
Like I said back in May when we were talking about upload, it’d be nice if the File System API were un-deprecated and developed for non-Chrome browsers (or, better, replaced with a less-verbose Promise-based version). It’s completely reasonable for a website to want to operate on a directory of files (eg. a mod manager for a computer game like https://moddingofisaac.com/), and forcing them to operate within a browser-dictated sandbox makes filesystem access more or less useless.