On reflection, I've shifted my probability estimates around, so here's the short version of my comment.

And forgive me, but I hate rot13, so please don't read this comment if you haven't read the original novels and don't want to be spoiled for them.

I am certain - the human sort of certainty, where you can still change your mind - that the euthanasia metaphor from Book 6 will be recapitulated in some way in HPMOR. I am strongly confident that Dumbledore is suffering from plain old age-related cognitive decline and that it won't be dealt with metaphorically. I'm expecting Grindelwald to show up in a villain's cape at some point. I have a clue, not crushing evidence, but telling, that Dumbledore will be involved in his return. I think these things fit together neatly in any case - he wants assistance, and someone wants to volunteer. I don't have a better candidate at present. We'll see.