The only reason I would like to see Ness return is because I've been so accustomed to him from the past two games. I've played Earthbound, but I didn't really l ike it. However, like I said, I have grown to like Ness from his inclusion in Smash. Heck, that's how I learned about Earthbound in the first place.
I do think it would be cool if he could be another "Luigified" character. However, looking at Lucas's moves now, I think it would be too close of a match. Think about Luigi in Melee (and in Brawl too). First, look at the Mario Bros. special attacks.
Fireball - Mario's flies downwards and bounces, while Luigi's will remain straight. This enough of a difference to distinguish the characters apart.
Jump Uppercut - Again, they are similar, but different. Mario's goes slightly diagonal and impacts with coins. Luigi's flies upwards, but is more powerful if you hit the sweet spot.
Tornado - In Melee, Mario and Luigi's tornado attacks were very similar. However, since Mario has a new FLUDD move this should further destinguish the individual brothers. I'm also betting that Luigi will have his Poltergeist Vacuum to suck characters in. If that's not true, he still will most likely recieve another down B move different than Mario.
Cape and Missle - Obviously these attacks are the most different than the other specials they have.
Now, Mario and Luigi's physical attacks were similar, but they were noticably different. Their fsmashes, fairs, and dashes to name a few. This is how a "clone" character can become their own.
Now, Ness and Lucas could act the same way. It's a longshot though. The part in the post that mentions "up until now" really puts another nail in the coffin on whether Ness will return. However, let's do the same analysis. Granted we don't have much info about Lucas, but judging from the screenshots and descriptions we have enough to make a reasonable guess.
PK Blast/Freeze - The execution looks very, very similar. The only exception would be that Lucas can freeze you. The change in element though I think is enough of a change, like Mario and Luigi's jump punches.
PK Fire - Ness's fire would travel downward diagonally in the air, and create a lasting pillar of fire to trap enemies. Lucas's remains horizontal in the air, and seems to be more of an explosive blast. This is a subtle change, but I think it's enough of a difference.
PK Thunder - This is where it gets shaky. None of Mario and Luigi's specials are totally the same. Again, we don't know how different this attack will be from Ness's, but this looks like it will function exactly the same.
PK Magnet - Again, this is way too similar to Ness's. From the picture it looks as if the magnet only covers the area in front of Lucas though, instead of all the area around Ness. It's the same move, only modified very slightly.
The biggest thing that I think would make Ness and Lucas playable individually would be their regular moves. Ness has some cool moves himself, like the baseball bat and yo-yo. Lucas has taken those away and has taken a more Zelda like approach by using "magic." Lucas also has the rope snake to use too, which Ness never had.
I think the big deal breaker is the lack of difference in special moves. In my Mario/Luigi comparison, the brothers share similarities in only two of their moves -- fireball and uppercut. This is assuming that Luigi's down B is changed to something else, which is a reasonable assumption I think. Now, Ness and Lucas have all four moves that are similar. There are no special moves that really set them apart. The Mario cape and Luigi Rocket for example are very different. I just don't see that difference with Ness and Lucas. The only thing that could set them apart are their physical moves. That, or if Ness gets a makeover.
Have I ranted enough? Sheesh. Anyway I'd hate to see Ness go as much as anyone else, but you have to know when to let go. If Ness is revealed on the dojo you bet I'll rejoice. Am I going to lose any sleep over it? Heck no! Still, I will miss him if he goes, but I will welcome Lucas with open arms