In a brief post to the halo.bungie.org forum's discussion of his last update, Matt noted that

Adding IK to death animations is still in the preliminary stages. It won't be used for impact animations.

He also added more hints about that new weapon which, he'd said earlier, was once suggested on the HBO forum:

The weapon ideas comment was intentionally super-ultra-mega-vague, even for me. Think in terms of secondary abilities and that may help narrow it down a bit. :-)

To read the whole thread, go here.