Hi!
Hi php 5.5 is still probly years from being minium in mediawiki due to so many users use php 5.3 and 5.4.
The users should really seriously consider upgrading. 5.3 is EOL for a year now (which means, not even security fixes for a year) and 5.4 is going EOL in 2 months. If any of these sites are public-facing (and due to the nature of wikis, many of them, to some measure, are), running out-of-support software may not be that good an idea.