I wouldn't mind that at all. Even if people don't like his politics, him becoming president is very historic. It was a great thing for our nation to have him elected. Even having Sarah Palin as VP would have been historic. Unfortunately, I doubt Mt. Rushmore will ever be added to. I think it is going to stay as is.
Mt. Rushmore wasn't the greatest piece of rock to begin with; now there's no geologically stable part of the mountain left in which to carve it (that's why TR is sunk so far back). No face will ever be added to Mt. Rushmore. They'll need another mountain.
And so shall Obama summon one forth from the crust of the Earth itself, for He is the Messiah, and the planet itself bows to his mighty whims. Carve! Nay, it shall already be perfectly sculpted!