In a recent post to his site Fabian Schmengler has proposed a PHP 5.3 "Death March" in an effort to try to drop PHP 5.3 compatibility for applications and encourage the growth of PHP 5.4 and beyond.

An alarming large amount of websites still runs on PHP 5.3, which does not get updated anymore since 2014/08/14, after one year of “security only” support. In other words, the next critical security hole will only be fixed for versions above 5.4. By the way, active development of the PHP 5.4 branch was discontinued on 2014/09/14. it’s already in the “security only” phase. On 2014/08/28, PHP 5.6 has been released, on 2013/06/20, almost 1.5 years ago, PHP 5.5. So, by now, in the year 2014 everybody should work on PHP 5.5, right? [...] Almost half of the Alexa Top 1M Sites that run on PHP, state the version 5.3, ca. one quarter even 5.2, which is not supported since Jan. 2011. PHP 5.2.17 even is the most used patch version in this statistic.

He goes through some of the thinks might be contributing to this drag in adoption including the slow migration of official Linux distribution packages and the incompatibility of applications and frameworks with newer PHP versions. He makes a few suggestions of what different groups can do to help the cause - developers, project managers and hosting companies. He provides a list of things that are either deprecated in 5.4 or have been completely removed.