These are in widespread use for a few applications. Probably every bank has at least one iLog instance running for enforcing business rules. Another one is "complex event processing", where a RETE engine makes it easy to aggregate small events into larger events. Also, a few efforts, such as Inform7 and Clara have tried to push the boundaries of programming for non-experts and real-life applications.
It is interesting, however, that the technology is not further applied, and a deep analysis of that could be worthwhile. For instance, RETE networks can eat "callback hell" situations for lunch, much like the complex event processing case. Instead, however, we are seeing one awful Javascript framework after another, and coroutines pushed as a very narrow answer to the problems on the server.
Note that all forms of A.I. have ties to optimization. For instance, usually when you train a neural net you are minimizing some kind of an error function. Drools (and iLog) both have optimization frameworks, etc.
The recent discussion of "superintelligence" has been marked by both a lack of imagination and any awareness of previous work on the subject. For instance, Rules engines are a fairly direct answer to "AI Safety" and "AI Ethics" problems that there is so much handwringing about. Most areas that require computers to be "creative" amount to some kind of multi-objective optimization, and even if rules can't make a system good, they can at least prevent the worst abuses.