If you compile it for yourself you can already enable it since 2.68 IMHO, but I suppose there are reasons why it's still off. I've read somewhere that it's possibly enabled in 2.72 or 2.73, but that has been said for 2.70 too.

Brecht van Lommel left the Blender project for working on the Arnold renderer, so development may go somewhat slower with Cycles.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.