Drupal 8 will come out in late 2013 or early 2014, by that time PHP 5.4 will be at least 1.5 years old. Probably PHP 5.3 will not be supported anymore by php.net, but Linux distributions will be stuck with it as a default a bit longer (e.g. Ubuntu 12.04 LTS will use PHP 5.3 and will be supported until 2017, though there is a well respected and easily available ppa to get php 5.4+ on 10.04 or 12.04).
If we keep going with the 3 year release cycle for major Drupal versions, Drupal 8 will be supported until Drupal 10, which will probably come out in 2019 or 2020.
Are we sure that we want to go with PHP 5.3 (first released 2009) until 2020?
Issues that would be helped by requiring PHP 5.4
Iterators can't be (easily) unit tested without phpunit 3.8 which requires php >= 5.4
Would be improved if we can rely on Native SessionHandlerInterface from PHP 5.4
and aim to improve DX.
Taking advantage of traits (in php 5.4) in these issues will help us remove required, but unusable methods from entities without possibly adding duplicate code.
Survey of major distros to see what PHP they support in 2013
It appears that all popular Drupal environments include PHP 5.4 [or above] by 2013. (list obtained from "Page Hit Ranking" on http://distrowatch.com/)
Operating Systems / Tools
- 1and1: Default to 5.4, also offer older versions
- A Small Orange: 5.3-5.5 - with 5.3 being phased out in 2014.
- Bluehost: 5.3-5.4
- Dreamhost - PHP 5.2 - 5.4
- Gaiahost.org php 5.3-5.4
- Gandi - PHP 5.4
- GoDaddy: 5.4 scheduled for November, 5.5 available soon after
- Greengeeks: 5.3-5.4
- HostGator: 5.4 targeted for early 2014
- Inmotion Hosting - PHP 5.2 - 5.4
- OVH - PHP 5.3, 5.4, 5.5
- Purley Hosting - PHP 5.4
- Site5: 5.3-5.4
- Vevida - PHP 5.3 - 5.5
- Webfusion - PHP 5.3 - 5.5 (on request)