I think this is a great call out, and you're correct. One example that comes to mind is that NFSv3 doesn't support flags on the rename() operation (such as RENAME_WHITEOUT), which means that you can't use them as an overlay upperdir (which is desirable for building container runtimes). To solve this, we're working on a custom protocol that we intend to place in the Linux kernel which will expose a broader set of features than we can get in NFS. As I tell people, this is the worst version of Regatta that will ever exist -- we're going to make it better every day.
