for me, there's 3 things that could possibly make me cancel my preorder:
1) if TOR would require an origin account in any way to play the game;
2) if they for some reason decide that they want world PvP to be an integral part of the game and don't add PvE servers;
3) if a personal emergency happens that would make me unable to properly enjoy the game.
what could make you cancel your preorder?