Same thing they showed for the Kethric trailer; some clips of gameplay with cool moments and thematically appropriate voice over. Only this time about multiclassing.
Im not really sure what that would be ...
I mean ... cool moment from Wizard casting fireball, is exactly the same as for Wizard/Rogue casting fireball, or Wizard/Fighter casting fireball, or w/e else ...
I mean, multiclass may be cool feature, but just as ASI ... its usefull, but invisible. :-/