Currently 100% expecting Arle Nadja and a FE3H newcomer. Arle has been highly requested in Japan for a long time, and SEGA has been suddenly pushing Puyo Puyo in the West ever since the Swtich released. That's too out of the ordinary for something not to be up. FE3H was successful, and it's Fire Emblem so yeah.
Doomguy, and a Granblue Fantasy newcomer have better odds than most other characters.
Doomslayer is likely in because the franchise is popular in the US, it laid the groundwork for the genre, and based on Sakurai acknowledging John Carmack as the father of FPS games, even if he's just talking about games casually, he's making it pretty obvious that he would take any opportunity to get Doom represented in Smash.
Granblue Fantasy is owned by a company that Nintendo has stock in, it's huge in Japan, likely the only mobile game Nintendo would choose for representation in Smash. Expanding Smash to reach mobile gaming audiences seems like something they'd do, and Spirits mode seems to derive much of its mechanics from mobile RPGs like Granblue Fantasy. Phrases like, "more collaboration," "expanding the world of Smash," just scream we're adding a newcomer bringing mobile game representation to Smash to me.
Geno is a dark-horse candidate. Maybe he wasn't high-priority enough to make the base roster, or the fighter's pass, so they threw his spirit in as a consolation prize. But now we've got more DLC on the way, meaning they possibly had an opportunity to expand his representation. Considering he is third-party, one of the remaining current long-time requests still not in, and was considered for earlier rosters, he may have a shot. The question is, will they just bring him back as a Mii Costume, or a fully-playable character?