Here's something which nobody has yet pointed out - Dumbledore knew for many years about the curse which Voldemort put on the DADA jeorb, so why did Dumbledore give Snape the job? Did he know that Snape is really just an evil git, but this was the best way to get rid of him? Did Snape need an excuse to get out of the school without alerting Voldemort himself?
What I'd like to know is the following:
1) Voldemort opened the Chamber of Secrets 50 years before Harry's second year at school. AND...
2) He was in his fifth year at the time. So he graduated 48 years before Harry's second year, or 47 years before Harry's arrival. AND...
3) He went to work soon after at Borgin & Burke's. He must have held that post for about two years in order to rise from clerk to buyer, and to get that close to Hepzibah. So he stole the locket 45 years before Harry's arrival at Hogwarts. AND...
4) Dumbledore said that 10 years elapsed between his disappearance from Borgin & Burke's and his return to Hogwarts. And the curse on the DADA position began on that day. SO...
That's 35 years between the time the curse begins and the time Harry begins taking Dark Arts lessons from Quirrel. Where on Earth did Dumbledore find 35 teachers in that entire time span? Wouldn't word get out that the position was really, REALLY,
REALLY jinxed? How many other teachers ended up dead, with addled brains or exposed as undesirables in the 35 years before Harry showed up?
Also, I think that it is theoretically possible that Harry will be the next Defense of the Dark Arts teacher. Yes, he has vowed that he won't go back to Hogwarts. But since the board may be pushing to close the school, and parents are worried about the safety of their kids with Dumbledore gone, the only thing that will appease everyone is if the Dark Arts position is offered to The Chosen One.
Harry might bend to McGonagall's persuasion if the position gives him special dispensation, such as unfettered access to Dumbledore's portrait and permission to Apparate anywhere to pursue the Horcruxes when he's not in class. And he already has experience teaching the position...
Working against this theory is the fact that the curse against the DADA position is still in effect. A lot of people know by now about the Harry vs. Voldemort prophesy, and putting these two facts together will ensure that placing Harry in that position will definitely set in motion the final confrontation between the two. And although we,
reading the books, know that the final confrontation will take place at the end of Book 7, the characters
in the books don't know that. They'd be extremely reluctant to force an early confrontation, trying to put it off as long as possible.
My thoughts, anyway.