PHP 5.5.0 is still in alpha testing (that is, it hasn't even reached beta yet), so there's not going to be a timeline on that any time soon.
As for an upgrade to 5.4.x, PHP fiirst-dot version upgrades can be very disruptive, so they tend to be put off until they really can't be avoided. (Moving to PHP 5.3, for instance, meant that a lot of people lost their sites altogether because of Zend Guard/Optimizer version incompatibility. Those who were using third-party software/themes that could be downloaded in a different encoding could re-install and reconfigure, but anyone who had used the old site builder — and let's keep in mind that there are a lot of people who use those silly things — was outta luck.) It also means ensuring that cPanel and Softaculous support is in place across the board, so there are external dependencies to consider as well. 5.4 may be skipped altogether, or it may be upgraded at the point where it fixes more than it breaks; you're going to have to wait for official word on that.