Well, it can't be NWN3, since Neverwinter doesn't exist in 4e. So I'm sure they'll call it something else. But it'll be intended to fill that market, I think as well. I do hope I'm wrong, I really have no intention of supporting 4e in any way, shape, or form.
Neverwinter while indeed "destroyed" in 4th ED does not mean that it could not be rebuilt. If I remember correctly, in NWN1, wasn't in a state of repair after Luskan attacked it? Personally I'd rather they abandon the "Neverwinter" name and start with Waterdeep Nights".
Though my feeling on what game it is... I'm almost certain Atari has approached both CDProjekt and Obsidian for D&D games. As for what game each dev was approached for, remains a mystary.