This "theory" is not true it has been dis-credited by HBO. DO NOT spread this rumor as truth. Watch the episode again. The actor who sits down in the diner is in the credits as "Man in the Members Only Jacket" he IS NOT credited as Phil Leotardardo's nephew. Nor has ever appeared in a previous Soprano episode (according to HBO). This is also a reference to the very first episode of the Sopranos which was called Members Only.
Who knows what happens to Tony? But he is not whacked by the so-called Phil Leotardo's nephew. Since Phil Leotardo's nephew does not appear in the episode.
I just wanted to clear that up. It was a false overservation that was put on the HBO website from a member of their forum. Like if somebody on this forum said "All Premier Designer bags 1/2 off at Neiman Marcus." Would you really go to NM or call first? Hmmmm....
You are right on the money! The man in the "members only" Jacket is not of relations to Mr L. He is simply just another "Member" of a family out to get Tony.
There is also no movie in talks as of yet.