I like this idea and I do wonder how it might fair on specialized niche search engines too, which likely would have much smaller indexes. I'm always looking for "simpler" architectures for small but custom web search, and I like what the author put together here!
Im actually looking into this myself. Adding facets isn't that hard to what's already there, and for smaller sites I imagine this could be a very inexpensive way to add search, albeit with slightly higher cost to add or remove items.
