I think we should migrate MediaWiki to target HipHop [1] as its primary high-performance platform. I think we should continue to support Zend, for the benefit of small installations. But we should additionally support HipHop, use it on Wikimedia, and optimise our algorithms for it.
In cases where an algorithm optimised for HipHop would be excessively slow when running under Zend, we can split the implementations by subclassing.
I was skeptical about HipHop at first, since the road is littered with the bodies of dead PHP compilers. But it looks like Facebook is pretty well committed to this one, and they have the resources to maintain it. I waited and watched for a while, but I think the time has come to make a decision on this.
Facebook now write their PHP code to target HipHop exclusively, so by trying to write code that works on both platforms, we'll be in new territory, to some degree. Maybe that's scary, but I think it can work.
Who's with me?
-- Tim Starling