Beautiful example of the sort of thing that I don't want to be locked out from doing by having the parser in user space.
However, one of my (unfinished) experiments was to have magic directories that show query results as their contents. One attribute of the directory (or even its name) would be the query string. That way even old software (like "ls") could use queries! Implementing queries-as-directories might require moving some things back into the kernel, or at least into some plug-in level.