For fun, I’ll speculate on what a Melee with six extra months would look like.
With six extra months, this would mean that Melee would come out around the spring or summer of 2002.
Roster: In terms of unique fighters, I’d say that Wario would almost certainly make it in given that he was the next one planned to be added. Also, I assume that Ganondorf would be more unique as there would be more time to make him stand out from just being a Falcon clone. Maybe he’d be like his Ultimate version but with a projectile. In terms of other unique newcomers, the only other ones I could see are Togepi and Olimar given that we have a few Mario, LoZ, and retro characters at this point, Diddy was in a grey area at the time, and Sakurai was hesitant to add a Kirby character at the time. I went with Togepi as it would promote the Jhoto region. Olimar was requested by Miyamoto, and Pikmin and Melee wouldn’t be as close in terms of release times.
Besides additions, Mewtwo and Game & Watch would probably be polished a little as their characters were clunky/broken.
For clones, the only one that I think would be excluded is Pichu as Togepi would be the promotional fighter instead. Otherwise, they should probably stay the same.
Stages: Most likely, Archanea, Icetop, and Sprout Tower would be added at the expense of Pokefloats. Also, I could see Wario getting a stage, but I cannot say what it would be, so I’ll use Rice Beach or Wario‘s Castle as a placeholder.
Game Modes: Outside of a more polished Adventure Mode, I don’t think this would be much different, but it would’ve been cool if six player battles could’ve been a thing.
Finally, the game would be more polished in terms of bug fixes and balancing. While the current competitive community would’ve disliked this version’s ganeplay, I could still see some of the competitive community sticking with this Melee given Brawl’s slow gameplay and tripping (a taboo for the competitive community)