it would be good if he could morph but he needs to kill the person and steal his/her soul

I think it would be cool if after using his soul steal special move, he can turn into the opponent.

That would be good, but very difficult to do. Think about the loading time... Whenever you morph, that kombatant's special moves, standard moves and fighting styles had to be loaded. Remember Shinok? Only moves were loaded not the looks. Before DA that was "easy" because there were no fighting styles and only 2D. Sadly I belive that even Shang would take part in Dcptn that won't be possible...