The biggest problem with it would be the horde is stil.. divided. Young warriors see garrosh ofcourse as there real leader and inspiration since they only know the blood curse and the struggle of the orcs as history. The Veteran warriors and shamans see thrall stil as the real leader of the horde as they both want to be done with the bloodshed and just want to stay in a place they can call home.
The other problem is killing a warchief never goes good in the books, for doomhammer it did but that was because blackhand was a puppet. but for thrall it would go in the history as 1 of the biggest faults ever + he made garrosh warchief so the only way is through Mak'gora.