I have for many years speculated that Gandalf's plan could have been to get everyone to Gondor and allow Sauron to besiege the combined forces of "the west" and then fly the ring to mount doom at the last moment. If this had been Gandalf's plan from the start, and if there were some hint of this in the book, then the rescue from mount doom would not seem like such an egregious plot device.

As it is, the story makes no sense unless one assumes that Gandalf simply figured all this out and said nothing (after all Frodo's disappearance after Boromir's lapse rendered the plan obsolete, and Gandalf wasn't there anyway). Again, if such a plan existed, there's no evidence Gandalf confided it to Aragorn. Indeed, a simple hurried exchange between Gandalf and Aragorn before Gandalf confronts the balrog could have foreshadowed the eagles and solved LOTR's biggest plot hole.