Some mythical persons that I would like to see. As most historical charakters are dead, the choise is somewhat limited.They have to be monsters, supernatural beings, have powers or "immortals". I added some suggestions how he/she could be used  :

Black Pete/Krampus: evil sidekick to Santa Clause (Imagine him showing up to give orders/news to Dresden)
The lady of the Lake: Arthurian folklore (would make a great handmaiden to the new Winter or Summer Lady)
Frau Holle: Germanic lore. Truthfully, I believe we have already seen her (Mother winter) 
Gilgamesj: Sumerian king/hero, Wise & powerful. (the true identity of Rashid)
Hafgufa: A giant sea monster from Germanic lore (I can see him attacking Demonreach)
The walking Jew: Christian mythology, Cursed to walk the earth for taunting Jesus (Perhaps he is trying to redeem himself so he helps the knights of the cross or thinks a sword will give him salvation so he tries to steal one)
Sir Galahad: Arthurian knight that found the Grail (perhaps picking up a sword again)
Maria: Mother of Jesus. (comforting Michael Carpenter after he hears his daughter was lost to the WG)
Nicholas Flamel: Great alchemist and the maker of the philosophers stone. But after featuring in a story with that other wizard named Harry, perhaps not likely. (Beer makers are also alchemists right?  )

Lets see if any will show up later on...

I don't think MS is Death, not really she might be part of the aspect of death for mortals, or she could be a goddess (or as near as a pure force of nature can be) of death like the Fate was, but I'm not convinced she's Death.

The Fae are (at least so far) based on the fae legends and Celtic/Germanic legends. So far, Jim Butcher tried to keep gods being gods and Fae/fairies/monsters/supernatural beings being monsters. The Four Horseman are more Christian/abrahamic in origin. So I would rule out that possibility. So If I had to guess we will have to search for a legendary character who is most fitting for the Mother(s). And the one that seems to be most fitting is Frau Holle (it is even believed that the European word Hell (and different variations in different western languages) is derived from this source). Here are some parts of what Wikipedia says about her:

In Germanic folklore as established by Jacob Grimm,[1] Frau Holda or Holle is the supernatural matron of spinning, childbirth and domestic animals, and is also associated with winter, witches and the Wild Hunt. 

Spinning
Frau Holda is matron of all of women's domestic chores, but none so much as spinning, an activity with strong magical connotations and links to the other world

Winter
While governing domestic chores, Holda is also strongly associated with the outside wilderness, wild animals and places remote from man. Frau Holda's festival is in the middle of winter, the time when humans retreat indoors from the cold; it may be of significance that the Twelve Days of Christmas were originally the Zwölften ("the Twelve"), which like the same period in the Celtic calendar were an intercalary period during which the dead were thought to roam abroad.[6] Holda seems to personify the weather that transforms the land, for when it snows, it is said that Holda is shaking out her feather pillows; fog is smoke from her fire, and thunder is heard when she reels her flax. Holda traditionally appears in either of two forms: that of a snaggle-toothed, crooked-nosed old woman, or a shining youthful maiden clothed in white. As the maiden in white, her garments resemble the gleaming white of a fresh mantle of snow.

Protectress of children
While Holda is generally described as unmarried, and has no children of her own, she is the protectress of children, the kind spirit who would rock a child's cradle when its nurse fell asleep. She is said to own a sacred pool, through which the souls of newborn children enter the world

As Water-Holda
Many pools, wells or fountains are associated with the water-holda (roughly translated) throughout Germany. She haunts lakes and fountains and is seen as a fair White Lady bathing in the water and disappearing, a trait in which she resembles Nerthus. Like Nerthus, she too drives about in a wagon, sometimes requiring the help of a peasant to repair it. When he carves a new linchpin for her, she pays him with the cast-off wood chips which turn into gold if he is wise enough to take them. Young women would sometimes bathe in the icy Alpine pools in the hopes of becoming healthy fertile mothers.

Leader of the Wild Hunt
In German legend, Holda held her court within the Hörselberg, and from this mountain would issue the Wild Hunt, with her at its head. The faithful Eckhart was said to sit at the base of the mountain warning travellers to return whence they came; he also rode ahead of the Wild Hunt warning people to seek shelter from the coming storm. While Holda in northern Germany is described as leading a procession of the dead, her close counterpart in southern Germany, Perchta, is described as being surrounded by the souls of unborn children, or children who died before they were baptised. This points to Holda's dual role as protectress of souls both entering and leaving this world.

Matron of witches
Holda's connection to the spirit world through the magic of spinning and weaving has associated her with witchcraft in Catholic German folklore. She was considered to ride with witches on distaffs, which closely resemble the brooms that witches are thought to ride. Likewise, Holda was often identified with Diana in old church documents. As early as the beginning of the eleventh century she appears to have been known as the leader of women and female nocturnal spirits, which "in common parlance are called Hulden from Holda". These women would leave their houses in spirit, going "out through closed doors in the silence of the night, leaving their sleeping husbands behind". They would travel vast distances through the sky, to great feasts, or to battles amongst the clouds

I am sure Mother Winter is Frau Holle...

So what is Mother Winter true identity? What's particularly annoying is the 'our' name, meaning the name should fit for both mothers.
Several possibilities come to mind: Isis, some Indu or sumerian goddess, or even the WG. For me it's unlikely: Jim said he may not use indu deities, and I doubt that the mothers are mere deities. And there is absolutely nothing pointing to Isis for instance, or the WG. They seem to be force of nature (Mother Summer "it's not your" world), beyond good and evil:

My Gueass: Frau Holle/Holda (some speculation suggest that the word Hell is derived from Frau Holle).

From wikipedia:

In Germanic folklore as established by Jacob Grimm, Frau Holda or Holle is the supernatural matron of spinning, childbirth and domestic animals, and is also associated with winter, witches and the Wild Hunt. Her name is cognate with Scandinavian beings known as the Huldra and the völva Huld
(...)
While governing domestic chores, Holda is also strongly associated with the outside wilderness, wild animals and places remote from man. Frau Holda's festival is in the middle of winter, the time when humans retreat indoors from the cold;

She would fit.

We are told that Kemmler used this exact technique of devouring spirits (not souls) as fuel for his own power, and the more powerful the spirits, the more power he gets from it; all in service to exposition of his evil insanity.

We Also know that memories are important to ghosts. No more memories, no more ghost. When sir Stuart shot the ghost, he used memories as a bullet. And he got "energy" back from the remains of the ghost. If I recall correctly, Harry did something similar while being a ghost. The fact that you can do something similar does not make you Kemmler.

Besides, We have been speculating that Kemmler could jump bodies like Corpstaker. It seems far more likely that he jumped bodies before he died than that he somehow was reborn in another body without the memories, drive and desires. Simon for example was fighting him and could be one of the people he jumped into (his disappearance/death later being a great way for him to return to his old dealings). Then again this does not explain how Kemmler returned the first time. It would help a lot if we had more info on Kemmler (besides how he did it  ). Things as, Did the returned Kemmler have the same body? Was he helped with his return? Were certain items important in the returning process? etc...

So I do not believe that Harry is Kemmler reborn. Evil Bob would have recognised Harry as being him. But you and others make a valid point that the darkness in Harry must be explained somehow.

D-E-D dead is Jim emphasizing dead and being cute at the same time.

I might be mistaken, but isn't "Dead, D-E-D Dead" also a movie quote?

Questions:
1) When Harry Soulgazed Molly he saw that in one of her possible futures she was no longer human with yellow eyes. Is there somebody in the Dresden Universe that has the same yellow eyes? How can you become such a creature (inhuman with yellow eyes)

2) Harry's mom can predict the ways in the nevernever. Time is fluent in the nevernever. Did this mean that Harry's mother could also predict the speed in which time passed or choose the paths and know at which speed the time passed.

What proof do we have that Harry's father was human? Ebenazar says he is mortal but we don't really know if he ever met Malcom. Yes, in Blood Rites he says something about Malcom having a good heart,

The there is the option that Malcolm was Harry's father (as in raised him) but not his biological dad. Maybe Harry's mom was already pregnant and Malcolm was so in love with Maggie that he accepted the child as his (after all, he has a good heart). It would give another spin to the story and we would have to find out who the father was and what...

We find out they're engaged in Blood Rites, Chapter 28.  I don't recall that the wedding date is on page anywhere.

Ok thanks!

Somehow I had the impression Harry was at that wedding (imagine Harry at the wedding with the family of Murphy). Clearly i am mistaken.

Harry says it would have to be something like an angel. ANd Uriel answers, "Yes, a fallen one."

Well Jim has stated that Lash was in Ghost Story but just under a different name...