Python and Ruby will be with us for a long time, but PERL and PHP will die an ugly death. Facebook has already abandoned PHP in favor of a PHP subset that runs on a modern VM platform (HHVM). We can't all do that, but we can adopt tools that run on the JVM or take on a well-designed language like Python or Ruby or Javascript.
On the JVM we have things like Grails on Groovy, Clojure and Scala which have strong development teams and visions for the future.
PHP, like PERL, just doesn't fit in any more. We have moved beyond hacks and incorporated computer science into our development platforms in order to save time and money and fossil fuels.