If LT becomes Warchief, where will he be stationed? Orgrimmar? Then are they going to replace him in Silvermoon? Would be lame to have the same PvP boss in 2 locations. If he stays in Silvermoon with his people, does Silvermoon become the new capital? Then who is going to be the PvP boss in Orgrimmar?
The easiest solution is make an Orc the new Warchief and copy/paste his abilities from Thrall or Garrosh for the PvP boss. Or just make it Thrall like they originally intended.