So,
this video happened. And in the first few seconds of it, you can see a movelist for Siegfried. It has the following moves:
Critical Edge: 236236 Right Trigger
Brave Edge 1: 3(Y), Right Trigger
Brave Edge 2: 4XB, Right Trigger
Something in Japanese: 66X
That felt really dirty to type inputs like that...for those that have trouble reading it, it's an Xbox controller, so X, Y, and B are equivalent to A, B, and K respectively.
There's not too much to go on, being as how Siegfried isn't even played in the video, and we haven't actually seen these moves yet. Or, maybe we have and we haven't realized.
On assumptions: I'm assuming that Brave Edge 1 is the one we saw from SCH, that is, the one that resembles SC3 SCH A+B. It would make the most sense. However, 4AK is a really weird input...I don't think he's ever had anything like that before, and I can't really speculate on what that might be.
EDIT: I have more for you here in
this video, but not too much. The second hit of SC4's 66KA is now its own move. Causes stun ("oww my face" fall backwards FUFT) on CH, it seems.