There is really no reason at all why Dravid shouldn't be able to open in test matches. In fact, despite where he has batted all his career, I've always felt he was a "natural" opener so to speak - I think he has the potential to be the best opening batsman in the world.
As it has been noted, this has been tried before. It really wasn't a horrible failure though - he scored two centuries in thirteen innings averaging 33.54. It doesn't look great at first glance, but when you take into considering that it was first tried in the late ninties and was a genuine failure at the time, it looks a bit better of late. In the last proper attempt he had at it - against Pakistan in 2005/06 - he scored 265 runs in 6 innings at 66.25 and notched up both of his two centuries opening.
There has never been much question over his technical capabilities to deal with it - only with his accustomed role and value to the team. In the past, the argument that he should not be risked in an unfamiliar position as India's best batsman was a valid one, as was the point that the next best opening option probably wasn't any worse than the next best middle order option anyway. However, Dravid's form over the last twelve months has not been great at all and he probably wouldn't even make the middle order on form alone. Add to that the fact that Karthik has failed of late, the fact that Sehwag is in all sorts of problems and the improvement as a batsman of Yuvraj Singh - Dravid opening makes all the sense in the world. I really hope he succeeds there, even as an Australian, as the quality of openers around the world is not great at the moment and I really think he could be high class.