Well, I agree that it would be nice for new people to read the earlier posts, but the amount of text on this forum is starting to get close to the size of the game itself
Just try to go back and read it all in one sitting.
So if anyone has an idea they think is new and they've at least skimmed over the previous pages, I don't see why they can't post about it. The way things are now (and knowing ryuukishi's writing style), I think there are no theories that are impossible.
And Ryuukishi himself told his readers to try all the bad theories as well, to see if you can stumble on a tiny part of the right one.
That said, I think any theory which denies the witch or Battler's theory outright seems very doubtful. After all, if you saw that Ryuukishi interview, he said that the Schrodinger's Cat analogy was actually supposed to show up in episode 5. If that is something close to the truth, then magic has to exist, at least until the battle is resolved.