I read this, and I have my issues with it. It says that Gandalf couldn't tell anyone else about the plan because it was a secret...which doesn't make sense. In the event that they were captured, it wouldn't have mattered whether or not the enemy knew the plan (because the mission would have been over). In the event that just one or a couple of them were captured...ok, Gandalf wouldn't have wanted those being tortured to say anything, but he had no reason to keep it entirely to himself. He could have told one or two other members of the fellowship who could be trusted. Are we really supposed to believe that Aragorn would tell the enemy their plan if he was captured, but Gandalf wouldn't? No, because I'd honestly trust Aragorn more than Gandalf with such information. And furthermore, Gandalf could have just told Elrond. The guy is in Rivendell, one of the safest places in Middle-Earth. If there is a single character in the series that probably has the smallest chances of getting captured, it's Elrond. And once again, he wouldn't let the enemy know what the plan was even if he was captured.
Besides, this entire concept wasn't mentioned at all in the books. The book is told through an omniscient narrator, so the reader is made privy to pretty much everything relevant that happens with the Ring. However, Tolkien didn't think it important to mention that Gandalf was hatching this plan with the eagles?
Yeah, no thanks. My theory on it? Gandalf is high on pipe-weed for pretty much the entire story, so he doesn't realize the most simple solution. If that isn't good enough for you, then It's just a plot hole.