Ok, I just got back from a screening of Catching Fire (better than the first btw) and definitely didn't expect my Pichu post to generate such response. I read all of the replies and rather than replying to specific people I will reply to the general points that were raised.
First off, I don't hate Pichu at all. Just because I don't want him taking one of the 5 remaining spots does not mean I hate the character. There is a middle ground between love and hate. I just think there are way better choices than Pichu, I don't inherently dislike him.
We already aren't getting every single part of Melee's roster back as Dr. Mario is merely a skin for Mario and Young Link does not exist (unless you consider Toon Link to be him...which he isn't). If they want to bring Pichu back in a similar way to Dr. Mario, as a skin for Pikachu, I am all for that. I know alternate skins will not be alternate characters, but technically Pichu is Pikachu's baby form anyways...so I'm pretty sure it could slide through as a loophole. If people are fine with the Dr. Mario costume then I don't see why this should be a problem.
In terms of some people wanting Pichu in as a joke character...I completely understand that. Joke characters are funny and it's fun to try to win with a character not considered to be innately good. The thing is, if they want to do a joke character I think there are better options than Pichu. Some people have been suggesting Pokemon Trainer/Red and I actually think he could be a pretty great joke character if they really want to make a joke character from the Pokemon Universe. Not to mention some of the work is already done for them there with his model, announcer call, css assets, etc. And if they want a joke character and don't need him to be from Pokemon...there are so many other options from Nintendo franchises available.
Another big thing I see people reply with is that the PMBR would, or could, make Pichu better to make him not so bad. This kind of goes against the fundamental principle people like about him though (that he's a joke, and thus fun to win with as an underdog character). He already has Pikachu's moves, making him better would make him even harder to differentiate from Pikachu. They could give him different moves, as electric pokemon can do a lot more than what Pikachu/Pichu have demonstrated...but then he isn't even the same character from a gameplay standpoint. Once you start doing that you may as well just use a different electric pokemon (at least) as that character is no longer Pichu.
Earlier in the thread I was having a conversation with someone about the Black Shadow/Ganondorf thing being bad because even though the moveset would stay the same (on Black Shadow), it would no longer be Ganondorf. Ganondorf would have a new moveset, and that wouldn't be right for the Melee vets who mained him. Well, this seems to be the opposite argument as this Pichu one...and you really can't have it both ways. Either a character who changes their moveset is a different character or they aren't.
For the people who want Pichu in just because he was in Melee, changing him like this would fundamentally make him not Pichu...and that would make doing it because he was in Melee completely pointless. At that point a different character is a better option. So, with that in mind, if Pichu came back due to his spot on the roster in Melee...it really only makes sense for him to come back as an underpowered joke just like he was then. But, if he does come back as that then he is just a not-as-good Pikachu taking up a spot that a more creative idea could occupy.
This is my "problem" with Pichu taking a spot. It goes beyond whether we "have 7 Pokemon reps" already or not. In the end that really doesn't matter that much, you guys saying that are right. But what does matter is if the character is interesting, and Pichu just isn't. Again, I don't hate him, but there are so many promising and great options out there...including for a joke character that isn't just a weak Pikachu. If Pichu makes it in at all, it should be as a Pikachu skin. It really is a total waste if he takes a valuable spot that could go to an idea that would better diversify the roster.