We are in process of implementing an upgrade from PHP 5.4 to PHP 5.5 as PHP 5.4’s final end of life approaches in a couple of months time.
This should be a pain-free migration, as PHP 5.5 has only some rather obscure incompatible changes from 5.4. It will be possible, if you have a reason why 5.5 can’t be used, to keep your site on PHP 5.4 (we will still have it available) – just let us know.