Giving a REAL answer to your question I think from the way Dan talked it is going to be a somewhat large knife, but large can mean different things. It could mean

1. Long like the scizzy
2. thick bladed like the Zilla
3. broad bladed like the Zilla
4. long and broad bladed like nothing we have seen from Dan before.

Overall though, unless he is messing with us, I think it will be a large (relatively long) broad bladed Zombie Decapitating chunk of steel!