I disagree. No, TNO is not a Chosen One: He chose himself to pursue immortality for his own reasons. The Chosen One trope stereotypically requires that whatever makes the main character special was beyond his/her control and was not "random." This includes heritage, blessing, prophecy, etc.--some external force. So TNO was not a Chosen One, but he sure was special in another way, and Ravel recognized that. (Gawd, I loved Ravel.)
Baldur's Gate was Chosen One... although there were kinda two of them in BG1, and the trope was actually dampened in ToB because you discover a bunch of other Bhaalspawn.
I don't think we need to worry about PE because the general plot update already tells us our PC is a victim of circumstance, which I much prefer over touching any of that One claptrap. It would really fall under #3 with a twist--"wrong place at the wrong time" given the update wording.
Agreed. The original incarnation of The Nameless One certainly wasn't chosen or prophesized. He was simply a man who made a terrible mistake and wanted to buy enough time to make it right. That snowballed into a threat that potentially threatened the planes, but in the end it all came down to choice. Your Nameless One didn't have to end anything. You could go to the Fortress of Regrets and not even solve the problems that were present in the story. Definitely not a chosen one.
I'm not sure that your character being in the wrong place at the wrong time excludes you from being that sort of important character, though. Whatever it is that you witness could potentially leave you and the people around you fundamentally changed. Maybe you are jam packed full of souls, or maybe your soul is so badly fragmented that you should have ended up dead. There's still plenty of room for this story to take that sort of direction. We won't know until we get more details.