That looks a lot like the Ultimate Hammer!
Thor in the movies has been closer to the Ultimates version than the classic power wise so some version of that seems likely. I will actually prefer that to the ax only from the comics. I don't have a clue about this new hammer in the comics but it will probably be sans anything other than basic abilities or just a conduit for Thors power. If they aren't going to return the real mjolnir I wish the new weapon did have an upgrade in looks similar to Stormbreaker. given that it looks like groot supplies the handle in the movie I think it may be supplied by the world tree in the book.