You know how everyone said the Sleeper was going to be impossible and be the rarest "exotic" too bad it wasn't because the FoAF is still the rarest Exotic, even though it's Year 1 it's still one of the rarest exotic weapon to get. Even though I haven't got Sleeper, some people said it didn't live up to its hyped which is even more sad.
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Foaf is jade rabbit so that part of your argument is invalid. "No time to explain" is the only weapon we know of that is still be be discovered. If you look at the blueprints though I think there are a few more that will be unlocked later. (probably around when heroic kings fall comes out) And on top of all of that there is at least one exotic armor piece per class that is still locked. Bungie has timed locked some items and it seems like they have also hidden a few too.