*I tried to keep things reasonable, but I'd say this is more an ideal roster than a proper prediction. 79 characters is a bit big after all.
*When laying out the roster I tried to keep it official looking and "clean" keeping it to an even shape (rectangle) and also making sure my characters were grouped similar to the official games. series with multiple representatives took priority on the left, in the order that there series first game was released, and then any gaps on the right were filled out by singe rep series characters in order of release. For series with multiple representatives instead of organizing the characters by when they were introduced to their series, I decided to organise them by smash bros debut order. and heroes first, villains second (eg: Mario and Luigi were in the first smash bros, peach and Bowser debuted in melee peach is a "hero" Bowser is a "villain" so Mario, Luigi, Peach, Bowser etc etc) 3rd party characters were put at the end of the list, but also organised by when their series debuted. and finally Mii fighters at the very end next to random.
*Yoshi and Wario were put at the end of the Mario series reps because on top of being Mario series characters, the also represent their own series.
*I tried to get a good balance of new characters for existing smash series as well as series that haven't been in smash yet.
*I may have gone a little Mario heavy which led me to removing Dr. Mario as a Clone and move him into being an Alt Costume for Mario, I felt out of him, Lucina and Dark Pit he was also the one who was the most... removable?
*Given that Donkey Kong and Zelda are fairly major franchises that didn't recieve any new characters in smash 4, i felt it was reasonable for both to recieve 2 newcomers this time.
*A lot of my characters choices were based on "this character is pretty popoular and has some demand for them" or "this character is inevitable" in Inkling's case. though i feel Inkling would fit well.
*Some of my choices were purely due to me liking the character and thus they may be slightly less likely choices
*If a character already has an amiibo from another game i felt this was a point in their favor for inclusion. (Inkling, Alm, Chibi-Robo and Qbby) but characters didn't solely get in because they had an amiibo already
*Out of any potential mario reps I felt that Waluigi, Captain Toad and Geno were the best choices.
*Waluigi is a mainstay of the series who could have a lot of potential for a moveset based on the wacky abilities he has in the various sports titles. creating tornadoes and vines and stuff. people who say Waluigi doesn't have anything going for him besides sports equipment just haven't done their homework.
*Captain Toad has become a fairly prominent character in the Mario franchise, appearing in most recent games. and even getting a game of his own. even Waluigi hasn't had that yet. his inability to jump could be problematic to making him work in smash. but he definitely has the presence to deserve inclusion.
*Geno has long been requested by fans and Sakurai had even considered adding him to a smash game at one time. there may be some issues with Square having the rights to him. but if Cloud and the Geno costume in Smash 4 are any indication, they may be able to work something out and make many fans happy.
*outside of Link, Zelda and Gannondorf, only a handful of characters in the Zelda franchise have reappeared in multiple games. among the more prominent are Tingle and Impa. and while Tingle's appearances are more consistent compared to impa who has been everything from an elderly granny to a slender mystic to a beefy bodyguard. Impa feels like a better fit for a fighting game than Tingle who suits being an assist trophy better. Sakurai would have plenty of different Impas to draw inspiration from. although personally i'd hope Hyrule Warriors Impa would be where most of her moveset comes from. Impa just feels like a fitting addition to me.
*Initially I wanted giant blue pig monster Ganon as my second Zelda newcomer. but felt many would reject the idea due to "Ganon" already being the final smash for Ganondorf. so I went with my next best choice from the franchise, Vaati. he's had multple appearances and would be a good secondary villain rep.
*Bandana Dee deserves to be in smash. (I'm a supporter of him if you couldn't tell from my username
) I could go on for AGES about why he deserves to be in. but I will just leave it at. Reoccurring character with unique moveset potential for a popular series. if you need any more convincing. just head on over to his support page.
*Krystal is a pretty heavily requested character. I admittedly don't know much about the Star Fox franchise so she is in there more due to me seeing her as a popular and potential choice. and also because I doubt her moveset would be anything like the other 3 star fox characters.
*Takamaru was always an interesting character to me. and after playing his game, its a lot of fun. he'd be a great new retro rep. and Sakurai has said before that he'd want to include him as a playable character but felt his lack of popularity outside of japan made him not be a viable choice. after his appearance in smash 4 as an assist trophy, getting a mini-game in Nintendo land. and having his game released on virtual console outside of japan. this seems like less of an issue now, so i think it's about time Takamaru had his chance.
*Isaac and the Chorus kids both seem to be pretty heavily requested and feel unique enough that I decided to include them.
*Chibi-Robo is in a bit of an odd place, he's had several games released, and even has an amiibo. but his series hasn't done super well. he may not be super likely to get in. but I feel he is deserving of a chance in smash bros. especially since that may help rejuvenate interest in his franchise. there's tons of moveset potential and he'd make a good fit. it all comes down to whether or not sakurai decides he is worth including. but I feel he is.
*Qbby may seem like an odd choice, but his series has been quite well recieved. enough that he even got his own amiibo. and despite the 3rd game in the series being referred to as the last game. there's been some hints lately that a new game may be on the horizon. there hasn't really been much in the way of eShop representation in samsh (outside of Dillon being an assist trophy) and personally i feel that out of all nintendos eShop IPs, BoxBoy is one of the better ones and Qbby has some good potential as a smash character.
*Inkling, Springman, King K Rool and Dixie all feel like they are inevitable and guaranteed to be in at this point. (maybe less so Springman, but I still feel Nintendo will want to promote their newer IPs)
*Starfy is an oddball left field choice for an unexpected character. not much to say other than it'd be a surprise.
*My 3rd party choices i tried to keep to a minimum and I feel several smash 4 3rd party characters won't return for 5 due to licensing issues. so I kept some of the more major characters (maybe that's just in my eyes though?) and then included some new 3rd party characters.
*Banjo and Kazooie may belong to Rare who now belong to Microsoft, but the characters have a history with Nintendo and a very loyal following. and there's been claims from Microsoft that they'd be cool with Banjo in smash, so why not? plus, it's been my dream to play as Banjo in smash since i was 11. just give him to me dammit
*Bomberman really feels like he would fit in smash, and given his series was revived as a switch launch title i feel he has a pretty good shot at getting in.
*A final fantasy rep in smash was a good idea. but I personally don't feel Cloud was the best choice. Black Mage, to me, feels like a much more fitting choice for smash bros. especially given his appearance in Mario hoops 3 on 3 and Mario sports mix. he has more of a connection to Nintendo than Cloud does.
*Shantae was chosen due to being a fairly popular/requested character. and I felt she has a better shot than Shovel Knight due to having more of a History with Nintendo. but she is probably my least likely 3rd party choice.
*Decidueye and Alm were added since i felt those franchises were major enough to get another character next game, despite how many characters they both already have. and Decidueye and Alm seemed like the best choices AT THIS CURRENT TIME. however, if smash 5 ends up being several years away, we'd have possibly moved on to a new pokemon generation by then and the upcoming Switch Fire Emblem game may have come out already, in which case those 2 would be replaced with characters from the newest games.