Btw. ownCloud 6.0.1 was released yesterday: http://owncloud.org/releases/Changelog
God I love the idea of ownCloud so much but secretly hope it's not written in PHP. I run a wordpress site for 3 years, and one day a hacker took my site over with a bug from a plugin.
By the way, most CMSes on other plateforms assume you know the language , PHP CMSes dont, so maybe there is some effort to be made on these plateform to make thing easier or write better docs.
Wordpress would not be popular if it was in Python,Ruby or Java. Anyway the issue is with Wordpress plugin architecture , not PHP.
A clean plugin architecture would require some kind of DSL instead of plain PHP.