There are certainly few models extracted already by those who get themselfs into Beta but as i am not one of them i cant rly say how its packed yet i think its all in same engine as Starcraft II is so i expect CASC archive + M3 and those are formats that we can work with
if you want badly some models i would recomned contacting
bombowykurczak or rexxcraft or ellowas ( try 1st rexx i guess he gotta it definitly )
they all do WoW 3D Porn but actualy they have some models extracted ( widowmaker etc... )