We all know of one Raid so far, the Vault of Glass, but some newer members may not know of a [b][u]potential[/u][/b] second Raid. It was introduced to us quite some time ago, and I (because of this) think that most Raids, if not all, will be Vaults.
The second Vault we know of, and by that (potential) logic Raid, is Charlemagne's Vault.
Mind you, this is all speculation right now, but it seems likely.
Also, if you enough people need me to explain who Charlemagne is/was, I'll update the OP with information.
In Destiny, Charlemagne is what is known as a Warmind. Warminds are vastly powerful war machines built by the Traveler (Charlemagne is on Mars). The Warminds created the Exos before the Darkness attacked. They seem to have helped us with our defenses during the Collapse.
Ad astra.
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That seems very plausible. My personal speculation for the second raid is the Hellmouth. Here's my reasoning: We now know a little bit about Destiny's first expansion, titled "The Dark Below". I can't remember the exact description, but it has something to do with facing a hive fortress deep below the surface of the moon. Longtime Destiny followers might notice this sounds a lot like the Hellmouth, which was revealed in one of the game's [url=https://m.youtube.com/watch?v=eAbpZfqE8r4]first trailers[/url]. And a raid is definitely a good thing to headline an expansion with. Now, seeing as how Hellmouth was marketed as being in the game so early (it even looked playable), why would they pull it from the retail release and save it for the expansion? Well, it's possible the expansion's description refers to something else, although it definitely sounds like Hellmouth. [i]Or[/i] Hellmouth went from being a strike to a raid, it's just as likely as your speculation of Charlemange's vault seeing as how that was originally believed to be a strike as well. Of course this is wild speculation, I could even be proven wrong in the beta if Hellmouth shows up in it. Regardless, let me know what you think!