My ideal roster. Well okay, here we go: I tried to make it half-way realistic but I understand that everyone has their own biases and so it's very possible that my roster is waaay too in favor of things I like.
That being said, I decided to go with my ideal of the "smash 64" Which I half consider a joke since Smash first came out on N64, but it would also be a good final roster size since 64 would fit nicely into tournament yada yada my preferences already.
First of all: I made sure to put the mii fighters in there own slot. I feel like the next iteration will keep them, but just like this iteration I feel like the mii fighter may not be considered an official character, which I'm okay with since that gives me the wiggle room for the 64 characters.
Second of all: I kept third party reps down to the three included in this smash. I really do not feel like these three need any further rep in smash as of now. Maybe in future my mind will be changed but as of now I'm sticking to that.
Now, going to the top. The Mario franchise is pretty much dominating the roster, but every addition they've had has managed to be pretty unique and interesting. As such, I think Waluigi and Captain Toad should be the final two Mario characters to join the fight.
Donkey Kong has gone too long without the other two characters being included, so I believe both should make the cut. Dixie and K Rool would both be interesting to play as. Villager and Olimar should return, but their series don't need any more reps in smash in my opinion.
The third row focuses on Zelda. For too long they haven't had a good newcomer. Admittedly Sheik and Toon Link I feel contribute to why we don't see a new rep. So I believe Sheik should be replaced by Impa, who could take her moveset. From there, both Midna and Ghirahim should join. Yes they are popular characters that only existed in one game, but I feel like just because they were in one game doesn't hold them back from joining. Sheik, remember? Finally Captain Falcon and Ness. With both of their series ended as of right now, there's no need for more reps from either series. Sorry Lucas.
Kid Icarus in row four I gave one more rep and replaced Dark Pit from this smash. This is because I believe someone will pick of Kid Icarus and give us a new iteration (Hopefully good) between now and the next smash. As such, I believe Viridi would be the best newcomer since she will most likely return in the next game. After her it would either be Medusa or Hades, and just to avoid over repping the KI females I think putting in Hades would be fun. Plus, at least for the moment, Hades in the main villain and not Medusa. Following it is Metroid, and I put in Ridley because at this point he just needs to be in. I also added in Dark Samus, because my friend (I haven't played the series enough) tells me Dark Samus is almost entirely different and could easily have a unique moveset that would be different from the main samus. You'd have to deal with the similar look of the characters, but that's nothing new or difficult.
The next row I added back in a third star fox rep, but Chose Krystal over Wolf. With her staff she really could have a unique moveset, and Falco could remain so long as they change his FS to his arwing instead. (I can't remember, is it the arwing now?). The Kirby series meanwhile seems to want Bandanna dee, and if a series like KI gets four no reason to deny Kirby a fourth either. Plus a spear could be a cool moveset. Little Mac returns.
Pokemon. As one of Nintendo's biggest sellers it really should be close to Mario in reps. In fact I'm pretty sure Pokemon has outsold Mario on several occasions. However there aren't many more to add so I tried to focus on popular and unrepresented pokemon types. First of all Sceptile for a grass strater to finish the 'trinity' which I think is a smart idea. Then I chose Gardevoir for the Psychic typing, and Gardevoir for the dragon and ground typing. I would possibly choose Scizor for bug and steel typing if Jiggs were to be replaced.
Next is my favorite series Fire Emblem, and it was really hard not to try and over represent them. I kept Marth, Ike, and Robin. Then I chose Lyn. As the first hero in Fire Emblem the Western audiences saw, I think that would be a nice nod. Also since she wields a japanese Katana she could have a really good sword moveset that set her apart from Marth and Ike. However she would definitely need to be the last sword user. So next I chose Tiki. Tiki is now a reoccurring character and a Manakete (Dragon person). You could mix her with some dance-style movements like Ninian from FE7 for attacks, along with maybe a transformation or FS for her dragon form. Finally I think the Blakc knight would make a pretty good villain rep. He'd be slow but he'd be a spear user, to contrast the light and fast Bandanna Dee. Maybe he doesn't flinch until he hits a certain percent or something for a character gimmick. Shulk would obviously return and Isaac should be added as a Golden Sun rep. that series is far too good to die out. and even if it does he deserves it like Captain Falcon and Ness got their spots.
Nothing changes in the final row.
No, I did not forget that alts exist. They are pretty hard to show off though and the roster maker doesn't have many doubles to work off of, so I'll try my best.
Dr. mario for Mario, Mr. L for Luigi (With de papered appearance), Daisy for Peach, Captain Toadette, Dry Bowser for Bowser, the koopalings for Bowser jr. and finally the yoshi colors are enough for Yoshi. Rosalina doesn't require an alt.
Wario already has an alt, Waluigi could maybe have a sports outfit alt, Funky could be a Donkey alt, now diddy, dixie, or K. rool alts come to mind. Female Villager for Villager, and the return of Alph for Olimar (I forgot about him when making the alts).
Dark Link, Fierce Diety Link, and SS Link for Link swamos, Maybe a terta style and Hilda style alt for Zelda (Or HW), and maybe a Ganon style alt for Ganondorf. Midna and Ghirahim wouldn't really have any alts I could think of. Falcon could have a Black shadow Alt and Ness could have a Lucas alt.
Next in KI. Dark Pit for Pit, and Maybe Medusa for Hades. I originally put Pandora in there as an alt but I can't think who she'd make a good alt for so eh. Samus doesn't really need the alts since I focused more on adding character, but a metal ridley would be interesting and a light suit true alt for Samus maybe.
Woolf could make a Fox alt pretty easily and Leon could be a Falco alt I think. Yarn kirby for Kirby maybe and Waddle Doo version of Bandanna dee maybe. The only Pokemon with an alt would be Lucario with Mewtwo I think, since the two have had similar movesets and it could work well enough.
For Fire Emblem, a Lucina alt for Marth and a Female Robin alt, and a Hardin alt for the Black knight since the two would be similar characters. Maybe a Fiora alt for Shulk (Though I haven't played Xenoblade so don't quote me on the viability of that) and a Matthew alt for Isaac. Male Wii fit of course is another one.
For the 3rd party characters I figure giving them an alt wouldn't be THAT bad in the long run, so I chose Ms. Pac-man, Bass, and Shadow. I think those characters are relatively popular and close enough to the playable character that a viable alt could be made. Also you can't forget custom moves are now a thing.
So this concludes my long winded ideal smash roster. How viable is it? I have no idea. But hopefully I entertained you with the idea, and at the least you think a 'Smash 64' would be pretty cool too.