So, before I dive in, a few caveats. First, this post will contain spoilers for the main quests of several TES games. Second, please feel free to treat me as a lore-dunce, and tell me the flaws of my arguments. Third, however-- if you do so, please offer substance in your critique. It doesn't do anyone any good to say, "Alduin is not Akatosh", unless you offer some sort of argument to help explain why or why not. Thanks!
Premise 1: The "Metastory", the story about/behind the story, in Daggerfall, Morrowind, and Oblivion is about the Towers and their respective stones being destroyed (or destroyed-ish, whatever that's worth).
a. Daggerfall was about Numidium and control over its Stone, the Mantella. I'm not sure exactly how to deal with this in the context of the dragon break, but I think it's fair to say that Numidium was destroyed, and the Mantella may have been destroyed-ish. Nu-Mantia Intercept certainly implies that Numidium was dis-created.
b. Morrowind was about the Red Mountain/Red Tower and control over its Stone, the Heart of Lorkhan. The Heart of Lorkhan was destroyed, and the Red Mountain/Red Tower was destroyed-ish.
c. Oblivion was about the White Gold Tower and its stone, Chim-el Adabal, the Amulet of Kings. The Amulet of Kings was destroyed. I would argue that, from a metaphysical perspective, White-Gold Tower was destroyed, because it's stated in-game that the barriers between Oblivion and Tamriel has been destroyed, which sounds like the metaphysical destruction of the tower, to me.
Conclusion: If the Metastory is consistent, Skyrim's main plot is-- in some way-- about Snow-Throat and the destruction of its Stone.
Here's the problem: it looks like Snow Throat wasn't destroyed, and we didn't hear anything about its stone. What's going on? Let's first tackle the second-- what is the Stone of Snow Throat?
Premise 2: Snow-Throat has a Stone.
a. Every tower has a Stone. This is confirmed in Nu-Mantia Intercept, Letter 4.
b. Snow-Throat is a Tower, in the metaphysical sense. This, too, is confirmed in Nu-Mantia Intercept, Letter 4.
Conclusion: Even if we can't know what the Stone is, we know that Snow-Throat has a Stone.
Premise 3: The key part of Snow-Thoat's Metaphysical Form is that it's only half-there.
a. Per Nu-Mantia Intercept Letter 8, "Every dawnmaker Tower takes a myth-form."
b. Snow-Throat's myth-form is "a mountain whose apex is only half here".
Conclusion: We shouldn't expect the Stone of Snow-Throat to be fully present; there's something metaphysically half-there about it.
Premise 4: Alduin is an Enantiomorph of Akatosh
(This is going to be extremely contentious. I'll try to keep it straightforward. Wish me luck.)
a. The best way I know to describe an enantiomorph is a mirror image. If you see your reflection in the mirror, that reflection is obviously not you, and yet (assuming the mirror is clear) it certainly is you. Imagine if your reflection could be sentient, as well. Is your reflection you? Yes, and no.
b. Alduin being the "firstborn" of Akatosh can simply mean he's the first reflection/enantiomorph. Thus, this is coherent.
c. The book, "http://www.imperial-library.info/content/skyrim-alduin-real", seems to be a tongue-in-cheek critique of those who simply say, "Akatosh and Alduin are different, thus not the same!" It's more complicated than that. Sorry. They're not two separate dragons, and yet they are.
d. Akatosh-as-we-usually-know-him could, per http://www.imperial-library.info/content/forum-archives-michael-kirkbride, "time-scheme against his mirror-brother of the Nords, Alduin, to keep the present kalpa-- perhaps his favorite-- from being eaten." Sorry if this bothers you. Feel free to toss it out if it does. Welcome to the plot of Skyrim.
Conclusion: Alduin is an Enantiomorph of Akatosh.
Premise 5: Alduin is (gasp!) the Stone of Snow-Throat!
a. The metaphysical key to Snow-Throat is that it's only half there (Premise 3). An enantiomorph, a mirror-reflection, is only half there (Premise 4). Sounds like Alduin is the perfect choice!
b. We destroy Alduin, and he's about the only thing destroyed in the MQ. This should be a pretty significant signifier, right here, if I'm right that the Metastory is consistent.
c. Snow-Throat has a stone (Premise 2). Historically, we've always encountered the stones, and major plot elements hinged on them. Aside from Alduin, I'm not sure what else would qualify.
d. White-Gold Tower and the Amulet of Kings metaphysically helped serve as a barrier between Nirn and Oblivion. Alduin metaphysically helped serve as a barrier between Nirn and Sovngarde. Now that Alduin's out, Sovngarde is more readily accessible. You might think that's good; I'm unsure. It's certainly debatable.
Conclusion: Bad news, friends. We destroyed another Stone. Three cheers for the Wheel falling apart.
Thoughts? Comments? Suggestions? Approval? Ridicule? Fishy-sticks? I appreciate your feedback!