World is moving fast, and new programming languages emerge and get adopted quickly. People get used to the toolset, and after some time start longing for new paradigms and ideas.
Functional programming is one of the biggest trends of the recent years in programming, and quite soon, if you don't know any functional programming language, your market value will decrease.
Clojure is a contemporary LISP, functional programming language with immutable, persistent data structures, running on JVM. For Rubyists, its really easy to start working with Clojure, since many things in Ruby world help to understand FP paradigms better.
Learn about Clojure tooling, and hear the story of migrating off Ruby stack to Clojure, about reasoning behind such a decision, how Clojure has changed the way we write Ruby code, approaches to concurrency and code structuring.
"how Clojure has changed the way we write Ruby code, approaches to concurrency and code structuring" this by itself should make an interesting talk :-) I don't know how other feels but I think this quoted sentence is more than enough to fill the presentation time with substantial points.
Perhaps we wouldn't want to see how to migrate away from Ruby(during a Ruby conf:-) , but rather about the learning we can bring into Ruby and the learning we can give to other languages.