The question isn't whether we should replace filesystems, but rather if we should move core file system services *into* the filesystem. That is, should we embed all of the things that locate does into the filesystem? My answer would be "no" (I prefer single-task entities where possible), but making a filesystem "hook" wouldn't be bad (i.e., trigger X when a file is updated, where X might be an indexing operation). Perhaps we should standardize more metadata, where it is stored, and how it is accessed. There's nothing wrong with storing that *somewhere*. Whether it is the filesystem or elsewhere is a bit of an implementation detail.
"When the only tool you have is a hammer, you tend to treat everything as if it were a nail." -- Abraham Maslow