The availiable image is still based on Debian 7 (wheezy), but isn't there a Raspbian image based on jessie?
The official image include Wolfram Mathematica. Wolfram Mathematica currently only works on wheezy. If Wolfram Mathematica ever works on jessie I'd expect the official image to change to jessie.
There is an unofficial image here: http://gnutoolchains.com/raspberry/jessie/