When Eko died and whispered his final words to Locke, he announced them as "we're next." As confirmed in the November 6th podcast, Eko's final words to Locke were "you're next." This provides some ambiguity, though: Eko, in saying, "you're next," may have just been referring to Locke. If Eko meant "you all are next," Locke's interpretation would be correct - it refers to the Losties as a whole, or the group who went on the expedition to the Pearl.