I've been peekin' in on this thread for awhile, and finally registered to post.
I don't know the degree to which this has been pointed out, but Lucas's moves--even the ones said to be the same--are quite different from Ness's.
PK Fire- Shooting straight forward in the air may not seem like a big change, but as someone who uses that downward angle ALL THE TIME, I say it is. Personally, I think the move's better when it aims downwards and allows for more traps and surprises. Why change it unless it's to make Lucas stand out as different? The explosion is also angled forward more, making certain kind of escapes trickier. In other words? A different move.
PK Freeze/Flash- They operate on the same principle, but are really completely different moves. One freezes, one instant KO's, and PK Freeze seems to come out much faster than PK Flash.
PK Magnet - Lucas's is set forward more, leaving him vulnerable from behind, (or so it appears). Ness's has always encircled him completely. The two moves may also have different speeds of activation/deactivation.
PK Thunder/Recovery- Now, this is just speculation, but Lucas's positioning when he uses this move makes me suspicious. He seems surrounded by much more energy than Ness ever was, and is posed in such a way that makes me think he's not going anywhere. Could it be that Lucas doesn't fall in mid-air when using PK Thunder as a recovery? The before/after shots don't show enough of a difference to verify one way or the other on this, but I just have a feeling ...
I also wanted to mention that so far Lucas doesn't have any yoyos, and wields a stick instead of a bat.
To me, there's just too many differences. If Lucas is Ness's replacement, why should he play like a completely different character? Why change so much if Ness isn't in the game? It just seems like they're trying to define him as different from Ness so that including both is worthwhile. Also, there's certain other characters I fully expect to return who haven't been confirmed yet, (Falcon, Ganondorf, Luigi), so having Ness confirmed so late, or else not officially confirmed until he appears in the game, seems a strong possibility.
I also find Onett's return encouraging ...