The 5d2 doesn't have this, although I think the MagicLantern firmware does include focus assist, including contrast indicators (I think). I'm sure ML will come to the 5d3 eventually, but it's not a quick or easy processes. Given that it's a completely new Digic chip (ML currently only runs on cameras with Digic 4 I think), it's probably going to be very long, unless someone puts up some serious financial support for camera (or two) and pay one of the guys who really know what they are doing to work on it for a few months, minimum I'd guess.
