Sorry, I just lurk there.
I’m also fascinated by the theory that the potions puzzle (from the end of Sorcerer’s Stone) foreshadows the seven DADA teachers. In this theory, the three bottles of poison represent DADA teachers that turn out to be evil. The potion that lets you go forward represents a teacher who helps Harry greatly. The potion that lets you go back represents a teacher who hinders Harry, but who is ultimately an ally. (The clues imply that both Forward and Backward are good.) The two bottles of nettle wine represent teachers who neither help nor hurt Harry, and are ultimately of little consequence.
We can’t work the puzzle out for ourselves, because we don’t know the relative sizes of the bottles. (Too bad Rowling didn’t include a diagram or a description of the bottles.) However, Rowling does tell us that the potion to go back was in the bottle on the far right. This lets us narrow down the number of possible solutions to two:
Poison, Wine, Poison, Forward, Poison, Wine, Backward
or
Poison, Wine, Forward, Poison, Poison, Wine, Backward
Compare the second solution to the list of DADA teachers:
Quirrell—Lockhart—Lupin----fake Moody—Umbridge—???-----???
= (evil)—(useless)—(good)-----(evil)----------(evil)
-Poison----Wine------Forward—Poison--------Poison----Wine–Backward
There seems to be a correlation. If the pattern holds, then the next DADA teacher will be an inconsequential “nettle wine” teacher. The editorial on Mugglenet makes a convincing argument that Snape could be the seventh DADA teacher. He hates Harry, and has already failed to teach him occlumancy, but he’s still on Harry’s side.