I really like the idea of both Joxa and LFE (a Lisp on the Erlang VM!), but the main factor keeping me from using them for general purpose programming is the lack of "modern" collections. I would love to see them implement persistent data structures à la Clojure, with a unified interface for vectors, sets, etc. I know the Joxa stance is "make a good macro system and let users implement these" but as a (new) user, the task looks too intimidating.
The Elixir approach looks great, but it's unfortunately not a Lisp.
If you don't know much about PHP security, the single best step to secure your installation is to start by using the recommended PHP.ini file for a production deployment (often called php.ini-production or php.ini-recommended). This will set sensible defaults you can tweak for your own app.
Also, open_basedir is nice and should be used whenever you can but it doesn't match a system-wide chroot.
The Elixir approach looks great, but it's unfortunately not a Lisp.