To respond to the Pichu hate/disagreement, I leave this contribution to the discussion:
COMPLAINT:But Pichu is so weak, we don't need more useless characters!
RESPONSE: a few ways the PMBR can negate that statement.
-Recoil only happens if pichu misses her moves
-Pichu heals herself by crouching, a nod to how sleeping Pokemon can be healed in the main series
-to counter the damage mechanic, Pichu can be much stronger than it's previous appearance in Melee.
-give her something similar to Lucario's old aura system (where some attacks get stronger the more damage Pichu takes)
COMPLAINT: Ugh, I really think Pichu would be a waste of a slot, we already have like 8 Pokemon.
RESPONSE:
Seeing as how Pokemon is Nintendo's second largest(after Mario) series, it doesn't seem all that extreme. Also, bear in mind how popular Pokemon trainer was(despite being 3 characters in one)in vBrawl(unhacked).
COMPLAINT: Inclusion in Melee is a bad reason to introduce a character.
RESPONSE: She's the only character from Melee that has not yet been represented in Project M. Dr, Mario is an alt of pm mario(who was already a mix of melee mario and doc) and Young Link has had some of his moves integrated into Toon Link.
Seeing as how Project M takes inspiration, and bases content upon Melee(Brawl and 64 too)it makes perfect sense to represent yet another fighter left behind(Although this is no longer the case for all but pichu and young link.). Also, Mewtwo and Roy have recieved excellent responses, despite being forgotten Melee veterans.
COMPLAINT: But Pichu is unpopular!
Response: The Pokemon fanbase would love to disagree with you.