I'm considering that, just as Sakurai, the game uses the engine of Dragon King as it was the initial project. I'm also considering that Sakurai did existed, just wasn't involved with Smash, FE comes to West after Melee and KI gets the revival in 2012. My reasoning will only be for characters that weren't originally added to that game
I always thought that 64 should had only miscelaneous franchises(counting Yoshi and DK as separate series), I would also never add C. Falcon.
Reasoning:
Pit- I played the original, so, it was some bias
Marth- FE had a lot of games already in Japan, screw America
G&W- He is the beginning of Nintendo's history
I used a diferent method for deciding the roster: "Has the series got any new games recently?", with that, DDD and Diddy are added, some of the original Melee newcomers are also added, IC because bias, Muddy Mole as the Miscellaneous newcomer(and bias)
No third parties, I want Smash to be consisted of Nintendo characters
K. Rool- Would have been added in Melee, but Diddy had overprioritized him
Mewtwo isn't cut
Ridley- The Metroid series grew a lot between Melee and Brawl, as the main villain, he gets his spot on the roster
Villager- AC is a huge success, I will never understand Sakurai's "too peaceful"
I now focus on more miscellaneous series, but first Robin and Medusa are added for their series popularity
Greninja because I'm super biased
Saki, Shulk, Ray, Starfy, Little Mac, Isaac, Chibi-Robo and Takamaru(as the retro rep) are all added to represent more miscellaneous franchises and due to fan request, again, I'm a super biased game director, so Wonder-Red and Dillon are also added
The Yellow line ones are a funny idea I had, I call them the "Super Secret Characters", you can only unlock them after unlocking the initial roster and receiving the message that you unlocked all the characters(I'm such a troll, aren't I?), Mewtwo is unlocked after 40 hours of playtime; Skull Kid because of fan demand is unlocked by beating Adventure Mode on Hard with Ganondorf without using continues; Kraid is the most biased choice, you have to beat one of the Event Matches, you play as Ridley fighting other Ridleys in the smallest stage in the game for 3 minutes all of them have Super Mushrooms; and Goku is just to hear people's reactions once they find out that a character called Goku is in the game(if Sakurai taught me anything, is that you do everything for the laughs