There won't be a practical successor to Prolog. Clojure is possible because Lisp already is a general purpose programming language. Prolog isn't. You couldn't

There won't be a practical successor to Prolog. Clojure is possible because Lisp already is a general purpose programming language. Prolog isn't. You couldn't do many of the projects in Practical Common Lisp with it. For example, imperatively changing mutable state is really hard to do, yet a very useful approach to many problems.