In addition to being unsolvable from the perspective of the audience -- we don't know anything about magic!
Um, what do you mean by "unsolvable"? I would assume you mean "no one thought of it or suggested it," but in fact many, if not most, of the suggestions involved using magic in basically the way Harry did.
I assume he means: we are not in a position to have any confidence that a particular proposed magical solution is actually a credible one, at least from what we know that's internal to the story. (External things like what's been most clearly foreshadowed might give good reason for confidence.)
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 114, and also, as a special case due to the exceptionally close posting times, chapter 115.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)