There are lines and then there are lines...   It's all about the lines one chooses to color with in ...

Good luck with that!
I'm pretty sure the lines are fuego'd to ash or forzare'd to smithereens.   

... Do we have confirmation that Kumori was killed in DB? ...

AFAIK, we have zero followup-info about Kumori.

I tend (strongly) to believe that she isn't dead.  The Wardens would absolutely have fine-tooth-combed the site of that throwdown battle.  The corpse of a powerful practitioner like Kumori would have been found (ID'ed by magical items, casting paraphernalia, rune-scribed items, etc etc etc -- even if the aborted Darkhallow somehow "wiped" the magic clean, the physical items, carving/etc symbology, and so on... all would persist (albeit mundanely) & be recognized as-such by investigating Wardens.

Assuming Jim hasn't changed his mind, he's told us what the big choice was. It's at the end of Grave Peril when Harry goes to save Susan. Our Harry summons a bunch of vengeful ghosts to kill the vampires when he could have absorbed their power and lashed out. The other Harry does the later.

Do you have a source or cite for that?
Because while Jim told us happens "at the end of Grave Peril," the details of what that choice is (and how close to "the end" is close-enough to count) are oft-debated; but that one looks frankly-improbable.

Here's the only WoJ I know of:

Jim:  It’s going to be a different character because it’s going to be Dresden as he would have been if he made one choice differently, and the fallout from that effect on his life...
In this case it will be the big decision at the end of Grave Peril.

Exactly which decision is "the big decision" has AFAIK never been disclosed.  As I say, I'm happy to be shown to be mistaken, if you've got a WoJ citation!

Why do I find your "Harry absorbs the ghosts' power" proposal so improbable?  Because that would be Harry performing a mini-Darkhallow; just pulling the concept and the methods out of his hat (a hat, let it be noted, that Harry does not wear!) in the spur of the moment (and getting it right!) based on essentially zero experience with necromancy.  Later, we see how a pile of very-experienced professional necromancers hadn't been able to figure it out, all vying for the lost Word of Kemmler.  Harry is already too much of a Special Snowflake character; if he was also out-necromancing the professional necromancers, I'd find that far too OTT (just doing a mass-summons that way is already kind of a Big Deal).

My own main theory is that "the choice" was when Harry decided to let Susan walk away, at the very end of the book.  He made that choice out of selfless love for Susan, and as we've seen Love is a Big Freaking Deal in the Dresdenverse.  Had he instead convinced her to say -- applied emotional pressure or coercion -- out of his own selfishness and fear, the outcome could have been very different indeed.

My secondary theory is much darker... when Harry faced-off against Bianca, she offered him a choice:  to let her have Susan (already half-turned) as "recompense" for how Harry "took away" her own preferred pet, and Bianca would consider the matter settled.  Maybe Mirror!Harry accepted that choice.  I don't like it as well, but that's my emotional reaction; IMO there's several ancillary details that line up very nicely, almost looking like Jim intentionally wrote-in foreshadowing elements.
 

I really think Harry… is… Merlin… we will see. 

I think that'd have to be an off-stage event.  Harry is a long, long way from doing Merlin-caliber work.  Centuries at least; maybe even millennia (n.b. wizards don't have millennia-long lifespans).  Also, the Harry we have seen is frankly not smart enough; he's not stupid or anything, but (for example) Butters in a few months' tutelage from Bob had figured out a bunch of magic that had never occurred to Harry.  But Merlin-caliber magic is (that we've seen) extraordinarily complex.

The only way I could see it happening is if he gets some sort of extra magical knowlege, an Intellectus of magic or etc; and not on a "lab assistant" basis like Bob, as the struggles Bob has educating Harry are well-known.  He needs something internal.  As I recall, though, Bob wouldn't be enough -- not even Bob understood most of the rune-work, when Harry took him out to look at the island.

Merging with the Archive might do it; or with Demonreach itself (though AFAIK the Archive is bound to a female-descent bloodline, & likely has extremely-potent magic to prevent anyone else from interfering; and a Demonreach-merger would cause a tautological paradox:  Merlin creating Demonreach who creates Merlin).
 

... think we certainly haven't seen the last of Elaine ...

I'm sure we haven't!

Right before Harry and Carlos duel Malvora and Madrigal Wraith, he chats with Justine. He asks how she's up and around. She's more than a bit evasive I think. Sorry, I've been listening, so don't have the exact quote.

I'm sure this has been discussed, but Nemfected would explain it all, but it kind of pins down a timeline for infection of Justine.

Feel free to tell me it's been discussed and where have I been.  hehe

Cheers to all!

Brien 

Justine's Nemfection has been discussed, yes.
@Mira has an interesting theory that she has actually been Nemfected all along (or since very-early); I'm not convinced, but I think there's some evidence to support the idea, needing hardly any tin-foil for her hat (I've certainly needed much more, for some of my own crackpot notions!).

Papa Raith's Outsider-fueled personal anti-magic ward, and his porn-star-sorceress Outsider-summoning, Vito's Outsider-possession, Justine's Nemfection, all pointing to substantive Outsider activity within the White Court.

My theory is, Mab's primary interest in ordering Harry to marry Lara is to incite a "patented Harry Dresden Anarchygasm" amongst the Whamps, and proactively/preemptively expose more Outsiders.
 

... I think she is more suited to be Mab's replacement. The whole Winter Lady virgin thing would not be so nice for Lara.

The basic theory that Mab is considering en-Mantling Lara seems likely.

I think Mab has thoughts about which role would be better for Lara, but that -- being Mab -- she has specific plans for each of the Lady-Mantle and the Queen-Mantle going to Lara (depending on how things play out).
 

... Remember, the White Court thought that Thomas was a freak for loving a human in the first place- kinda like how people would look at a man that married a cow.

Love is not, broadly speaking, a thing that the White Court do.

I don't know that "freak" is the right term (I only recall that term being the Whampire term for wizards).
Unusual, for sure!

But they know the phenomenon -- protection via Love -- well.

And they know how to bypass it, if they really need to get to someone protected:  get one of their more-attractive Kine to seduce the protected victim; if needs be, they can apply their (non-contact) lust-enhancing mojo until the victim is "willing:"  being in Love doesn't mean being immune to the Whamp-mojo of heightened arousal.

If you aren't being all emo & addicted to the tragedy of the thing, Justine's solution seems kind of obvious; particularly from the POV of "sex is a tool" Whampires.