Just FYI, I made the original patch for these apis, John George added tests and took it over the finish line. Either of us can address the issues posed in this jira.
I do not quite know what ViewFileSystem does at the moment, but for non-Path queries is there no View-Root-Path it can fall back on?
Last I knew, ViewFileSystem does not support mounting a filesystem on the root (ie. /). Therefore, it's not really possible to "guess" a default since the underlying mounts may have different defaults. Even if a filesystem can be mounted on the root, returning the defaults of that fs is wrong since a union/merge/whatever-it-is-called mount of another fs may mean the intended path's resolved fs has different values. Basically a Path really needs to be supplied so the mount can be fully resolved.
Multi-mount filesystems break the semantics of these apis designed around the assumption of a single filesystem. Unfortunately this means there's going to be a hopefully not too painful bump in the road for users depending on these apis.
Unfortunately it also appears that getDefaultReplication() and getDefaultBlockSize() weren't marked as internally limited/private, yet externally deprecated. Otherwise users may have a better idea of why their code is breaking. We may want to consider adding those annotations.