The moment he'd say it I would be asking myself, "Alright, which of his sons came out to him?" Romney would just be another Rob Portman to me. If he ever did support same-sex marriage, it would be for his families selfish needs before ever caring about the actual nation.
Two things:
1. Your signature made me viscerally ill
2. Why put Romney in the same category as Rob Portman? And why does it matter which influential Republican(s) come out to endorse gay marriage? They're going to influence people no matter what, so...