Trader Joe's is an unusual company- they don't talk, the don't pre-announce locations beyond a couple of months, and they do not seek publicity. If you Google "Dan Bane", the CEO, the only interview you will find is with USC magazine, affiliated with his alma mater. Through a bit of perseverance, and a talk with the Regional Acquisition Manager, I managed to get a response from Dan Bane by email. In short, he reiterated that they do not discuss locations, and found the Manhattan market "tough" to find deals. That said, he indicated that Trader Joe's would "love to open a bunch of stores in Manhattan", they continue to "work on deals", and they would "love to open a great store in your area (Upper East Side)."
I'm not sure if that is a morsel or a nugget, but I would say there is hope for more Trader Joe's in Manhattan in the future, and on the Upper East Side. As for the 86th Street location, an email to the listing broker has not been returned, not like I would expect him to reveal details of a deal that he may or may not be working on. So, I guess the rumors will continue to swirl, just now with perhaps a tad more validity.
Trader Joe's Location Request Page