Drop support of too old PHP versions

I think the original poster is onto something.

PHP 5.3 is already end of life.

Is it a good idea to encourage people to continue with outdated and insecure foundations to what are generally a hostile environment on the internet at large?

I wouldn't say that. CentOS 6.x ships with 5.3.3 and it's considered one of the most secure, stable platforms out there.

If they jump to 5.5+ we'll have to rewrite our apps. Until it's necessary I don't see a point in forcing that on everyone who wants to continue using CI.