In an ideal world, this is the Smash 5 roster:
!0 Mario characters...9 vets, along with Toad as the newcomer after the capt Toad momentum.
4 DKC characters. K Rool will likely win the poll and get added as DLC this time. Dixie is a likely addition for Smash 5.
6 Zelda Characters, Impa joining the roster. While its possible Impa replaces Sheik, I doubt it after Hyrule Warriors. I can see here using some of her moves from the game, such as water elements, and using a giant sword.
Fire Emblem will likely get a new Lord. This would bring 6 Fire Emblem characters. Not sure if all of them will get in at launch, but Lucina and Roy are the first ones to get cut for vanilla....but would be very easy to make DLC.
7 Pokemon. Don't think any are getting cut out of the 6 veterans, While its possible Ivy/Squirtle/Pichu is there, I kinda doubt it, and a gen 7/8 starter makes the most sense to be added.
2 Animal Crossing characters. At first I added Isabelle, but I feel shes better suited as an AT than a fighter. Perfect nod to her in game role. AC is big enough to get a new rep, and I feel Tom Nooks can use the Tanooki Mario abilities to fight.
Takamaru, keeping the trend of one new retro character. He is the strongest candidate for this spot.
Chibi Robo, probably one of the most likely characters to get added in this game. 5 titles in the series, and going strong. He has many abilities that would lend to smash.
Isaac and Ray. These two are dream characters and probably won't happen, but hey, they would both have great movesets. Also considered Wonder Red here, but I feel Nintendo is just going to forget this game happened sadly. Golden Sun and Custom Robo had several sequels at least.
Chorus Kids: Id say a RH character is just about guaranteed for Smash 5, given the success of the series. Chorus Kids would represent the series well. Not to mention, the Chorus Kids were promoted to mascot in RH Best +, as they appear in just about every victory screen (Ala Marshal) and even have a role in the ending credits, etc.
Inkling: 100% confident they will be there.
Rayman: New 3rd party.
That would make 71 characters total. An increase from 55-58 some characters (counting DLC) in Smash 4. 14 of these fighters are newcomers (counting potential Smash 4 DLCs like K Rool). 7 new series repped (Smash 4 added 8 new series). Overall I'd say this represents the series well.