Seeing as how other people are posting their predictions and we probably aren't too far away from knowing the full-roster, I guess there's no better time to make my final predictions:
I believe there are three newcomers left for the base game:
Newcomers:
1. Geno (The timing and circumstances just seem right. Sakurai's confirmed he's taken character suggestions from the ballot and has stated in the past that he's wanted to put him in the games. Not to mention the Mii costume got special attention when it was shown off back in Wii U with the acknowledgement that Geno was popular. I'm gonna be a little surprised if it doesn't happen at this point.)
2. Incineroar (I may not like him, but it'd be silly to not consider him at this point. Game Freak is marketing him like no tomorrow and he has an easily realized moveset. He's the newcomer I feel most confident about on this list.)
3. Elma (A choice that I know has some popularity, but I do feel the majority are sleeping on. Xenoblade X was pretty well received, and Rex and Pyra's unfortunate timing kinda take them out of the running for base game IMO. If there's a Xenoblade character coming, I think Elma is the most likely choice, especially with the amazing moveset opportunity.)
Echos:
I've already made a recent prediction on Echos, but I'll lower my prediction of five to four and maybe narrow my ideas down a bit:
1. Isabelle [Villager] (Probably one of the most likely Echo choices we have next to Ken ATM. She's basically become the Animal Crossing mascot and is well beloved by its community. Making her an Echo of Villager makes perfect sense and adds another character to one of Nintendo's biggest franchises.)
2. Shadow [Sonic] (I feel pretty confident about this one. It'd more surprising it took so long for another Sonic character to show up, honestly. I also have a sneaking suspicion that if he does happen, it'd probably be thanks to the ballot; I imagine he probably placed decently on it.)
3. Ken [Ryu] (Let's be real, with all the Ken remixes we now have and him being the face of fighting game clones, he's probably the only character in speculation right now that's a near lock. Which is a shame, because I do not like the idea at all, lol. Would much rather have Akuma.)
4. Dark Meta Knight (I wanted to throw an out there choice on here for fun. I'm 100% positive this is not gonna happen, no matter how much I want it to.
)
I also believe we have seen the final stage count, and I believe Spirits will be an expanded Melee adventure mode with levels themed around Nintendo locations. If there is a story, there won't be SSE cutscenes; I believe they'll do what Mario Tennis Aces did and use the character models and basic text boxes, which is better than nothing IMO.
I'll revisit this after the final batch of info comes to see what I did and didn't get right. Can't wait to inevitably be completely wrong and get nothing right.