Well, he has endorsed Romney before.
I thought Cain said he was going to endorse soon when he dropped out of the campaign? I'm guessing he decided it was better to back a winner and withhold his endorsement till it becomes clear who the likely nominee will be. If Romney wins Iowa and NH, my guess is Cain will jump on the bandwagon.
Then you are a bad guesser, my friend. Romney is the least bold per Cain. :)