In the latest set of leaked images you can see the new Nemesis Strike Force detachments for Grey Knight FOCs. Also shown are some better images of things we have seen already.
Reading the powers that come with this detachment are
Brotherhood Commander, which includes re-rolling your warlord powers when this is your primary detachment.
Rites of Teleportation, which allow you to start rolling for reserves round 1 on a 3+. Also you can run and shoot the round you come in from deep strike. Very cool.
Also of note is that you get 4 elite choices and only 2 heavy support. This very much feels more appropriate to what we have from the previous grey knight codex. Definitely something I will be fielding.
Here is a link to the leaked pics