I've never really been anti-Pichu; I always loved playing as him and he was my favorite character while growing up, but I thought I'd throw in a few things to consider.
Pichu's advantages over Pika were largely small tweaks in physics. I'd call the momentum from his jump squat the most important of these changes. You also have a slightly higher grab range, smaller frame, much less weight, much less range, but slightly more protective hitboxes in general. I'm a little unsure about him actually being quicker than Pika, though. I don't think he dashes faster or anything, but if someone could point me to a movement advantage he has besides the jump momentum (which is a little situational with the addition of QAC) I'd be fine with that.
Overall, he did play different, but I wouldn't say vastly different. Pika and Pichu were still closer to each other in playstyle than most other characters. (that may just be my own personal strategy of using lots of SH Nair approaches)
Let's take a look at self-damaging:
Aerials: Nair is pretty much the go-to aerial for both of the 'chus. Punishing Pichu for using electric aerials won't matter much for differentiating playstyles because Pika doesn't use them as much either.
QA/Agility: Unless you don't want Pichu to Agility cancel (which would lead to inferiority problems with speed, range, combos, and probably additional stuff) Tacking damage onto agility is going to rack up the damage like none other. Is that really something that makes it interesting or just a useless feature? Pichu's lower KO% probably merits a better recovery anyways, I'd say.
Grab: The 1% pummel damage is ridiculous. Enough said.
I find it amusing that USmash is touted as such a unique power move from Pika when it still has less power, range, and speed than Pika's.
No buff should be given to his forward smash if it doesn't involve making it less SDI-able. That thing already has more base knockback than a Marth tipper Fsmash. It was pretty much the only move that had any sort of power advantage over Pika's counterpart, though, so I don't get where the "more powerful Pika" claims ever came from a while back.
Personally, I'm neutral for his inclusion. I play him all the time in Melee, and it certainly is a hoot, but I feel like if you keep that self-damaging aspect to make him unique, you'll open up a lot of problems and end up making a pretty massive overhaul to the character. Just don't expect the same playstyle if we ever get him, I guess. At that point I'd rather just have a different character, myself.