В Kohana 2.3.3 будет поддержка php4!

Цитата с форума Kohana:

great news, after many discussions and many debates on IRC, it’s been decided that future versions of Kohana will be PHP4 compatible (next version 2.3.3). Lots of users here complained about Kohana to be PHP5 only. That won’t be the case for the upcoming versions so that Kohana will suit the needs of everyone.
As you probably know, those changes will break backward compatibilities with older versions but it’s for the sake of the Framework.

В общем, ждите перемен и готовьтесь переделывать свои проекты.