As we are developing a php database interface for a project here at work and some related functions are being deprecated starting with php 5.5.x I considered upgrading our php installs on our servers and test if it works fine with our stuff.
As I’m using Slackware on my servers I managed to update the existing build scripts to build from a php 5.5.x tarball and I installed the new package on slackware64-14.0 and slackware64-current: in the next days some tests will be done with the new things we’re working on but, as for now, wordpress seems already to behave fine with it (also the plugins we use, but your mileage may vary).
If you want to test it yourself just get a copy of the sources from a slackware mirror: you will need two folders, source/n/alpine and source/n/php; then place the tarball (5.5.4 ATM) in the php folder, removing the old one.
To build it on the above platforms the needed modifications are very marginal and are listed in this diff
EDIT (23 november 2013): I just checked the current build scripts for 14.1/current (to build a newer version) and they have been adapted to build also php-5.5.x, so the modifications below aren’t needed anymore 🙂