My answer is largely based upon Christian anthropology (something that, unfortunately, I find many are shockingly ignorant of). Therefore, some preamble is necessary. Humanity is created in the image and likeness of God (Gen 1:26). Subsequently, it has been revealed that God is a Trinitarian being (Father, Son and Holy Spirit). The technical theological formula to describe the Trinity is three hypostasis (roughly translated as persons) in one ousia (which can be translated as nature or essence). Therefore, we — humanity — are a plethora of hypostasis in one ousia.
The implication of this reality is that what happens to an individual hypostasis (person), affects humanity as a whole through our shared ousia (nature/essense). This is why Christ's salvific work on earth is so effective — when He took on our nature by uniting his person to our humanity, His crucifixion and resurrection affects all of us. Our very nature and relationship with God was radically altered.
Since the Winter King knew of and had in his possession this Black Hand McGuffin centuries ago (as a member/leader of the Death Cult), there has to be a reason he did not take advantage of its magical properties when he could have all those years ago. The answer is based on the idea of ousia and is also the reason that the Winter King is willing to use the Black Hand McGuffin now. If and when he replaces his own hand with the Black Hand, his very nature will be irrevocably altered — he will cease being an elf.
Herein, though, is the way he intends so save the rest of the elves. By radically altering his ousia, his particular hypostasis will cease to affect the ousia of the rest of elven-kind.
I must admit that I know virtually nothing about the Eberron setting (I had left the hobby by the time it became the latest and greatest D&D setting); however, I cannot escape the art that accompanied it. One concept represented in these images that I find extremely intriguing is that of the Warforged — a magical elemental/construct as a character race.
I am considering the possibility of transforming the Winter King into something akin to this basic concept. There are several intriguing possibilities and consequences of this choice:
- While the source of the contagion may be neutralized, there are still members of the Winter Court in various states of infection. The Winter King (with the help of the PCs?) might have to hunt them down and offer them a choice: death or lose their "elfness" and become a sentient construct like him.
- Once the WInter King learns how to transform elves into sentient constructs, he may very well have a means by which to finally free the Winter Queen. She would likely insist that every elf who chose to have their souls bound to a bane weapon be given the choice to become a sentient construct (including and possibly starting with Hornet).
- As a result of all of this, the Winter Court will be heavily depleted and without a king for the first time in eons if not in all of history. There are very likely to be widespread political implications (will the PCs care/get involved?)
- There will be a new PC race-as-class available for players, the abilities of which I am still trying to hammer out. My rough draft includes a base AC7 (equivalent of +2 AC for you AAC junkies), the inability to be healed by divine magic, but the ability to burn equivalent arcane spell levels for healing (2 spell levels for every CLW equivalent?). This last as well as the arcane nature and knowledge of the original sentient constructs suggests that there will be at least a limited amount of arcane spell casting ability.
- Some working names (all of which will likely be used): Banes, Living Swords and Melltithians.
All that remains to see is whether or nor the PCs manage to get the Black Hand back to the Winter King...