My predictions for DLC:
Geno:
I heavily believe this is what Vergeben's second Square-Enix character is. Geno might be the only character that Sakurai has said he wanted to see playable that is not playable in Smash Bros.
Dante:
There have been two leaks on 4chan (perhaps the only two that might be legit) that point to him happening.
Banjo-Kazooie:
I think the information about Minecraft content happening is a sign that he is being planned. I feel strongly about this.
Rex & Pyrra:
Sakurai gushed about Xenoblade 2 on social media. The game is still getting significant content a year after its release. One of the obstacles thought to this character that few have talked about is Pyrra's design probably being a no-go for CERO (which is pretty stingy when it comes to risque female designs, as we saw from the removal of the Tharja trophy from Smash 4 3DS).
ARMS character:
This one I am a lot more iffy about than the above four. However, the game has proven to be successful. It will probably be represented by Spring Man with either Ribbon Girl or Springtron as an echo fighter.
The next set I am even more iffy on:
Fire Emblem Three Houses rep:
For every Smash Bros. game starting with Melee, there has been a contemporary lord represented with the game. It might be the same with Ultimate as well. There are four characters to choose from, but none of particularly different from what we have already seen in Smash Bros., or might not be well received by actual Fire Emblem fans when the game comes out. However, that did not stop Corrin.
Pokemon Generation 8 rep:
Incineroar likely taking up one of five fully unique characters slots shows just how much clout the Pokemon Company has when deciding the roster. It would not be a surprise if they demanded dibs on of Ultimate's DLC slots.
Bandanna Dee:
He is probably the most wanted newcomer among the Japanese fanbase, and the character himself has built up an impressive resume over the course of this decade. He would be an incredibly simple character to model.
Rhythm Heaven representative:
This is the last active Nintendo franchise without a playable character in Ultimate. Its very odd to me though that Sakurai did not refurbish his Chorus Kids idea for Ultimate. Maybe the character continued to have technical difficulties on the Switch? Its possible another character is chosen to represent the franchise.
Isaac:
As with Bandanna Dee, Isaac is probably the most wanted newcomer at this point among the Western fanbase. He likely did very well on the ballot. There is a strong rumor going out that a remake of the two GBA games is being made for the 3DS, and I could easily envision Isaac being released alongside this remake. However, it is also possible Isaac gets hit with the Assist Trophy bat once again for Ultimate.
The next set is technically possible, but I cannot see them getting in over most of the above ten:
Dixie Kong:
Probably the most iconic Nintendo character not yet playable in Smash Bros. after Toad. Unfortunately, while she probably did well on the ballot, she probably did much worse than K. Rool. Her fans are very quiet so even though she is among the most wanted newcomers out there, it does not seem like it (it reminds me of Roy). She could be a semi-clone, taking some of Diddy's specials and A-moves, but adding in her own hair attacks in as well. As with Isaac, its possible she ends up in a major NPC role in Ultimate (either as an Assist Trophy or part of Diddy Kong's unseen Final Smash).
Toad (Toad, Toadette, Captain):
Toad and Captain Toad having established roles in Ultimate might make them ruled out. It would be pretty odd for Toadette to make the roster when Toad and Captain Toad could not, however, her doing so could be a backdoor way for Toad to be in as well. Toad is probably the most iconic and well known Nintendo character not yet playable in Smash Bros.
Shadow or Tails:
Its very weird how Shadow did not end up as an echo fighter. Maybe there was a debate on whether Sonic's second character should be either Shadow or Tails? The problem with Tails is that he would need to be more of a semi-clone. With Shadow, he very well could be one of the few echo fighters made that is sold separately. It is going to be very interesting to see whether Shadow reprises his Assist Trophy role or not.
Impa:
Zelda has not received a newcomer since Brawl. Impa is a very realizable echo fighter of Sheik. However, I am not sure the idea of doing so has come to Sakurai or his team. However, I am not sure whether Nintendo plans to sell echo fighters separately (I could see the likes of Ribbon Girl/Springtron and Felix being packaged in with Spring Man and Isaac respectively).
Octoling:
Splatoon 2 is on track to outsell every single installment to the Smash Bros. series in Japan (its currently has sold over 2.5 million copies). The only other major Splatoon character that could fit would be the Octolings whom got a major role in DLC earlier this year, and are fully playable now. They could easily be an echo fighter of the Inklings and be very well received (especially among the Japanese fanbase), or be tweaked into becoming a semi-clone. It depends on whether Sakurai thinks Splatoon needs a second playable character or not, or if he thinks the Octolings are not distinctive enough from the Inklings. As with the above two, they might not happen since it is unknown if echoes will be sold as DLC outside of a newcomer package deal.