I heard that bungie had, in the works, a campaign setting (if you will) that they plan to feature numerous games in. Think elder scrolls. Everysite you have listed there says "fantasy" to me... It has been common belief that "heaven" is above us. Litteraly.
Dead orbit could refer to the fact that maybe whatever "gods" this setting has, are now dead and this new monarchy was brought about to adress the situation of their (now dead) gods. As Scat was so kind to point out, the seraphim aer an upper teir of angels. I looked 'em up on wikipedia and found that they are refered to as "The burning ones" (Their name litteraly means "burning one). It's not fire though that is the burning. It's like poison in your veins kinda burning... That makes me think of a silver tounged, power behind the throne kinda guy that has brought down this Pantheon of gods in order for these seraphim to take over the world...
SEVEN
Hasn't it been the running theme that bungie plans to take over the world?
Let that simmer in your brains for a bit...
It's funny, I have like a whole setting thought up now and have the urge to play some DnD... *Goes to find dungeon master's guide*