Long time back Sakurai stated that the Original 12 characters would return. (the true veterans)
The four unconfirmed are
Falcon- The only rep of F-Zero, no one could replace him as an alternative rep in the smash brothers series. Why would the remove a veteran, especially one representing a unique franchise.
Luigi-He put the Bros' in Smash Bros'. Thank you ROOOOY!.
Jiggly-Semi-confirmed (I'm skeptical) Unique gameplay, veteran, and his popularity SKYROCKETED after the release of the original smash brothers. How could they remove such a cute and cuddly puffball?
Ness-Semi-confirmed (again with the skepticism) Veteran, always been the only rep for Earthbound, unique gameplay...Also, if it makes sense to put in Jiggly, Falcon, and Luigi (which it does), then it woud NOT make sense to remove 1 veteran. I know people claim lucas has replaced him but it just wouldn't make sense. And is lucas a clone of Ness? It seems as much, but I would like to think these two will offer very different playstyles.
Fact is, Sakurai has stated hundreds and hundreds of times that Melee was rushed, he didn't have the time he wanted or needed to really perfect the game, but as stated in his interview, he has had all the resources and the best teammembers and ALL the time in the world to get this game right...he's not going to slump and disappoint the countless numbers of Falcon and Luigi fans. I can all but guarantee that.