At the time it mystified me, but knowing what I know now, I think the Walkers saw what Hydaelyn wanted them to - the coming of the Ascians and the inevitable fall of the Sixth Astral Era. Dalamud's descending wasn't part of the original plan, but the Calamity sure was; the final Ul'dah introduction quest was called Calamity Cometh, and the Imperial indoctrination of Ala Mhigan children includes the line, "Calamity is upon thee."
This seems quite reasonable. They don't seem to be part of her, just tied to her destiny. What that tie is I'm not entirely sure. The Crystals of Light seem to play their standard role of representing the elements that comprise the world. Hydaelyn, however, seems to be a little like IX's Gaia, the center of our network (however big it is) through which matter, life, and memories pass. If that's actually true, I also don't know. I just kind of took it for granted that Hydaelyn = Crystal of Light (seeing as she's a crystal who uses the word light in every sentence) and the Crystals of Light each represented an aspect of her lifeline. Beyond that I've got few ideas, never mind actual theories. When all else fails, I usually look back to Final Fantasy I - IV, on which Tanaka also worked, and especially III, in which he was the most heavily involved. Those appear to be the "roots" of XIV, and they do tend to line up with a lot of what I was saying before. You're right to question everything beyond that, however. I got nothin'.
EDIT: To add on to what you were saying, perhaps she's mustering up her strength through the gathering of the Crystals of Light, which were widely dispersed, well hidden, and impossible to collect, but are now in the hands of her champion. Perhaps they're kind of like Horcruxes, lol.
The same things happen when we see Echoes and speak to Hydaelyn, we kind of zone out and/or pass out. However, that doesn't mean at all that it's Echo-based. That could just be how we experience all aether-related visions. I always had a theory that Damielliot, an Elezen in 1.0 prone to passing out all over the place, was seeing something. Now, the STARSHOWER ... that's a mystery. My theory on that shifts a lot and presently my theory is that it represents the arrival of Ascians in our realm and that it's Hydaelyn's way of saying, "This. This is your enemy. This is bad." Evidence for that? Ascians are here and this one time a Starshower happened just as one showed up. Not a rock solid case, eh? On my to-do list is going through every single main scenario quest and looking for Starshowers, comparing them to Version 1.0's appearances, and seeing if anything stands out.
Tricky thing here is that it can be taken to support any of a number of views; I can't holdfast to it supporting any of them specifically. Again, I just take it for granted that the Mothercrystal of Light would choose a "heart of light" kind of person for the task, and the Crystals of Light would probably resonate with that. Like finds like, or in this case light finds light. We are meant to, after all, bring the Dawn of the Seventh Astral Era, according to the prophecies of Mezaya Thousand Eyes. There might be a deeper connection, and it might be the very one you speculate; I've just thought very little about it beyond the superficial, as "GO TEAM LIGHT!" has basically been the Final Fantasy Classic mantra forever and I assumed it was that simple, lol.
Reminds me of a few cases on 1.0 when we were able to reach into peoples memories and bring stuff back. In Ul'dah we brought back a flower handed out by F'lhaminn, in Limsa Lominsa we brought back a balloonfish left on deck during an aurelia swarm, and in Gridania we brought back a piece of the treant that was so angered by Yda and Papalymo's arrival. Even if you do know the source, being able to touch hearts, speak all languages, and unstick items in time is pretty anomalous.
That part I don't find so strange. Primals are made of three components: Aether, Prayers, Essence (and even that Essence part might just be "lots of similar prayers" or perhaps even beliefs and memories passed through the Mothercrystal and added to the Lifestream). The aether part is what comprises the physical being of the Primal and feeds their power. When they fight, they expend that energy, when they die, all that they've consumed is returned to the Lifestream to nourish the land. I also imagine that the Crystals of Light are more concentrated, more pure, and more powerful than any others of their aspect, more pure even than the flawless crystals ritualistically used by the beast tribes at the usual summoning ceremony. Fighting depleted her fuel, but ripping that crystal out of her blew a hole right through the tank.
Only because I have no idea. When we picked them up, we went into one of our visions in Hydaelyn's realm and they became part of that glyph. The NPCs, however, still refer to us as somehow possessing them, as if we could pull them out and juggle them at any time. I don't know if that was a symbolic unlocking of power and they're still in our pockets or what. It could be that we absorbed them, it could be that Hydaelyn pulled them into her realm and combined the rainbow into pure white light to banish the darkness, it could be that I've got them in a little Gym Badge case in one of my many SCH AF pouches. Sadly, I've nothing to contribute on that, so far.
Me, either. I forget who the first to bring that up was. It's a reasonable connection to make, it's just highly improbable given what we know. Primals use tempering as a way to gain worshipers and increase their power. There are no hints so far that non-primals can temper, that the Mothercrystal(s) are similar to primals, or that we are zealously devoted to Hydaelyn. Half the time we just look confused. I didn't seem much more excited about collecting the crystals of light and banishing the darkness than I did collecting ten adamantoise shell for that guy's ... uh ... stamina ... "potion." I'm an adventurer and a job needs doin'. I just happen to have an interesting client and little choice in the matter according to a few thousand year old book that I am in no way qualified to question when it keeps being right about me. Minfilia's way more on board than I am, and she's never even seen her.
I came across some translations of unreleased Version 1.0 quests a while back, and in one of them, the Company of Heroes actually does show up to fight Titan, and he actually does temper the belordofcrags out of them. One minute they're all, "From dust you came and to dust you shall return!" and the next it's, "Friend... Spare us your wrath, benevolent Lord of Crags! We live only to serve you!" As far as I can tell, the trick for tempering is just that the target holds the hell still for a few seconds while being deeply breathed on, which explains why it keeps happening to people being held prisoner. It's like you need to marinate in a good concentration of the haze for a few seconds, which makes sense to me, as it explains why Ifrit isn't just wandering across Thanalan like a 1970s flamethrower with a trail of everyone ever behind him as he marches on Ul'dah.
Also, we're 2/2 on Beast Tribe Quests involving non-tempered beast tribe members trying to save their race and its honor. Kobold and Sahagin come next. We'll have a lot more to go on when we see if the pattern continues.