I've been thinking and considering, reading and reviewing, and just in general starting to think about what I want to do with an expanded version of a story that I'm working on.
But anyway, I came to one idea that seems plausible, though completely untouched and left lacking in detail by Games Workshop. (As my friend put it, GW doesn't care enough to work on this material because 'GW has a raging hardon for Space Marines and basically nothing else.')
Reading about Slaanesh. I was curious about the reach of her will and saw mixed information, to me. In one instance, she's omnipresent, there at any moment of temptation, greed, lust, etc. But then in another, she's beatable by Nurgle, which to me implies a level of not being omnipresent. Those two things seem conflicting. I'd think that Slaanesh would be more interesting as a strongly present but not omnipresent being. Otherwise, I think everyone would be corrupted by now.
I also was curious about Spirit Stones so I was trying to find where their creation was mentioned. At first, I couldn't find it so I started hypothesizing about what is going on there. I saw an entry where it mentioned that Eldar create Spirit Stones so I was looking for the Path that was devoted to the creation of Spirit Stones.
BUT, then, I saw the mention that it is a perilous task to find more Spirit Stones. That to get a Spirit Stone is to go to the Crone Worlds within the Eye of Terror. That made me wonder if the spirit stones were made before the Fall, which I rightfully thought was weird because nothing about Eldar society before the Fall suggested any inkling of a want to make such a device.
Furthering my research, I saw a quote: "They are made out of psycho-receptive crystals called waystones." Well, that's great. What's a waystone? I didn't find it at first so it was a real head scratcher for me. But that's also when I came up with an idea.
What if Krivvin and all of his siblings (he has an older sister and younger twin siblings)... What if they were born with a Spirit Stone? An anomaly, born from desperation of his parent's out of love for their children to be free of despair, given form through latent psychic will. After all, the Eldar have a special spiritual and psychic presence in the Universe.
To my understanding, if anything like that were to happen; the Eldar of all would be the one to experience it. It doesn't seem incredibly farfetched, but is definitely an overly unique idea. Hopefully not absurd?
Thinking about it further. That means their spirits are a closed circuit, within the spirit stone by birth. I don't know what kind of durability it may have. I was thinking that it would be part of their body, like grown from bone or grown into bone. Kind of like a calcium deposit.
This would obviously make it a bit more involved to bring their spirit stones back to a Craftworld... That also made me think about their technology. Nothing really covers what they do with studying and tending to pregnant Eldar. It doesn't seem farfetched that they have perfected technology to be able to acutely analyze an Eldar body to know pretty much every aspect of their physiology. Simply, it would be no secret that these children were born with a Spirit Stone fused to their bone structure.
That's when my friend said that Spirit Stones are unique technology, essentially soul traps. If the Eldar have a way to detect and measure souls (which he is 99.9% sure they do), they'd be able to tell if something that doesn't look like a spirit stone is a spirit stone.
That's when I thought about something else. If a spirit stone were spiritually and physically bound to an Eldar throughout their life. It seems like it could grow alongside the Eldar as part of an Eldar's progression in life. As an Eldar's pool of psychic energy grew, it seems like the spirit stone might evolve with it. To what end? I don't know.
After I said that, I found another quote: "Waystones are brought back to the Craftworld to be embedded into a wraithbone core. It then grows into a larger spirit stone." It's definitely capable of evolving, when a spirit is inside of a waystone. That part is important, I think. A spirit is required to tap into the full potential of a waystone.
My friend pointed out "that this only happens after they die and when the spirit stone has a soul in it. Spirit stones are literally just empty vessels that trap souls." BUT! ... These Eldar are born with a connection to the spirit stone Their soul is inside of it already.
Then, I FINALLY FOUND IT. The little line that explains the creation myth of a Spirit Stone. "In Eldar Mythology the spirit stones were created by Vaul from the Tears of Isha. This is taken as a metaphor for the crystallization of the psychic energies of the Eye." CRYSTALLIZATION OF PSYCHIC ENERGIES. In my mind, it made an Eldar born with a Spirit Stone plausible. After all, the birth of Slaanesh didn't create one spirit stone. It created a well pool of energy that seems to constantly create spirit stones. Excessive psychic energy bleeding into the Materium is creating Spirit Stones.
That's also when I touched on Slaanesh being unable to touch the souls of those trapped in a Spirit Stone. Otherwise, she would be eating those souls too. That's the entire purpose of a Spirit Stone. To protect the spirits of the fallen Eldar from "She Who Thirsts."
My friend was thinking about what being bound to a Spirit Stone from birth would mean. He wondered if their souls in a stone, they could maybe do something with it. Like power and pilot wraithguards/lords.
Being encapsulated by a spirit stone means that their souls exist outside of the Warp. An eldar trapped in a soul stone would not be tempted by Slaanesh. It did make me think that it would hinder external psychic powers? I'm not sure really. To my understanding, psychic powers is a psyker reaching out into the Warp to pull out an effect and cause an external event.
My friend pointed out that when an Elder dies, they are put into the stones, which serves as their afterlife. The only way for them to interact outside of the stones if it they are made to be wraithguards or wraithlords.
I don't know if a living Eldar bound to a Spirit Stone would be able to use Psychic powers. I don't know enough about it and it doesn't really seem like they have anything to use to extrapolate further on this chain of thought. I was curious about what one might do with their own pool of psychic energy. Being able to draw that out and use it for smaller effects. It would seem to me like such an Eldar would have diminished psychic potential? Or at least, they wouldn't be able to do the awesome external super psychic powers. Their powers would be limited to the self only, influencing their individual bodies, minds, senses.
Doing so would draw out and push their psychic energy into the Warp. Basically, using Psychic energy would still draw attention like anyone else that uses psychic powers. Otherwise, their presence would seem to be largely concealed, if not completely withheld from the Warp.
... Just one long chain of ridiculous thought. It seems plausible and remotely supported. I didn't find anything that outright contradicts it. That none of this has happened doesn't seem like it is breaking anything. After all, as my friend thinks, "GW has a raging hardon for Space Marines and basically nothing else."
What do you think? I'd like to hear your input.

(I do not mean to offend or upset anyone! My apologies if I did anything to annoy. I'm just working out an idea. Feel free to critique, review, and debunk based on anyone's expert opinion of lore that I may have missed.)