Speaking of Mario Kart 8:
Do you think it makes sense to group characters from the Mario Kart roster into franchises like we do in SSB?
I think it's quite a point we could at least talk about as there is at least the possibility to group the characters into franchises as I did here with the MKWii roster:
Donkey Kong: Donkey Kong, Diddy Kong, Funky Kong
Yoshi: Yoshi, Baby Mario, Baby Luigi, Baby Peach
Luigi's Mansion: Luigi, King Boo
Super Mario: Mario, Peach, Rosalina, Daisy, Toad, Koopa Troopa, Drybones, Birdo, Bowser Jr, Bowser, Dry Bowser
Mario Spinoffs: Waluigi
(Wario Land/WarioWare: Wario) -> only Wario is in the roster from his own series
Original characters: Toadette, Baby Daisy
Others: Mii
Also: Since MK64, we got with every homeconsole installment a DK newcomer. In Double Dash we got Diddy and in MKWii we got Funky Kong. Why not take into account also the installments on GBA, DS and 3DS? Well, these always have less drivers than the "big" brothers on homeconsoles, so after all, for MK8 it doesn't really make sense to take other installments into account than the homeconsole ones.
Why could we expect another Kong for MK8? Well, Funky wasn't an obvious driver choice for MKWii and still Konno seemed to want another Kong in the roster. Because of Tropical Freeze, everyone is remembering Dixie(and Cranky) and Dixie would be a good choice in my opinion. I would be surprised if Konno were to not put Dixie in the game.
I also see a small chance too we may get another Luigi's Mansion driver because of Luigi's Mansion 2(Dark Moon) and the most obvious one appearing in both Luigi's Mansion games is Professor E.Gadd.
I also would keep Nabbit and Plessie into consideration. Nabbit could be the Honey Queen of MK8 having 2 appearances until now(just like Honey Queen in SMG1+2) while Nabbit even had a playable appearance in New Super Luigi U after his debut in New Super Mario Bros U. He's one of the new characters who could get a spot in the roster. Same goes for Plessie. Plessie can be put on an equal level with Rosalina(when MKWii came out, Rosalina only had an appearance in SMG1) having only one appearance until now. Plessie also has some level in SM3DW giving him some spotlight too. He's a character with some importance in SM3DW and while we would have the Sprixies as alternative characters from SM3DW, they are important for the plot somehow but you can't really say which Sprixie would deserve the spot. It's as if you were to request the koopa kids, you can't put them all in the roster and choosing one representative character out of them isn't that easy neither. Therefore I don't see the Sprixies getting in the roster and I think if there were a spot for a character from the recent Super Mario game, Plessie would be the choice. As we know from Honey Queen size is no argument to kick Plessie right away out of the list with possible newcomers.
Short version: I expect Dixie and I think Nabbit and Plessie are likely too. Prof E.Gadd may be less likely but I still think he has a chance of getting in the roster.
I really look forward to seeing the first newcomer being revealed for Mario Kart 8.