I think the Reef will have continuity in the lore of Destiny. Which is why I strongly believe we won't see any of the tower vendors in the Reef, but new vendors. Or maybe just one vendor.
The Queen, I believe, is also involved with The Nine so naturally Xur would be there.
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Please dear god, if the Reef just has more factions to grind I'll go insane... I really hope bungie is more creative than that.