Geno
+Sakurai acknowledges his popularity, so he must've done decently on the ballot
+He got a costume in Smash 4, probably related to that popularity.
+Square is already giving permission for Cloud to appear, and previously gave permission for Geno to be used as a costume, so they probably would not be a problem
+Since Geno is not really used for anything else by Square, they have less to "protect", so there would probably be less onerous restrictions put on his use, giving more flexibility and reducing work needed around getting Square's sign-off on design aspects, etc. (Presumably this is why Cloud/Sonic/Pac-Man's palettes are too similar to each other, and therefore kinda suck IMO)
+Geno would be relatively easy to design
+Super Mario RPG is an important part of Mario history and a highly regarded game
+While he's technically 3rd-party, he originated in a Mario game and has never appeared in anything but Mario games and Smash 4, which would perhaps relax some of the standards that would normally be applied to a 3rd-party character. He feels more like "a Mario character" than "a Square character"
On the other hand
-Geno is not relevant going forward. He hasn't had anything but a cameo since his game came out over 20 years ago, aside from his Smash costume
-Geno has a passionate fanbase, but it's probably questionable how wide it is (of course, other characters with that issue have gotten in)
-He's not iconic - outside of the Nintendo hardcore, would his inclusion mean anything to people? (again, other characters with that issue have gotten in)
-There are many characters that are some combination of more popular and more relevant
-He is still technically a 3rd-party, and aside from Bayonetta, they've all been pretty iconic characters. Even if Square might be less picky about how they handle Geno than Cloud, they might still not feel he's worth the additional hassle.
-To the extent that Geno is basically a Mario character (what else would his series/universe icon be?), Mario is not underrepresented...
-I'm not really sure how interesting he is in terms of his moveset. On the other hand, while we have Mega Man and Mii Gunner and Samus, his probable archetype has fewer members than the swordfighter archetype, say.
The bad news for Geno is that his lack of relevance will only increase over time, and I'm not sure that in 2025 or whenever the next Smash is, his popularity will maintain. Fewer and fewer younger gamers will have ever played his game (re-releases can help, but on the other hand, they're not bringing the Virtual Console to Switch...). This could potentially be a positive, as Sakurai might consider this as the best or only chance to include Geno (who knows how relations with Square will be when the next game rolls around) while feeling that some characters he passes up this time might be good inclusions next time.
Geno chances: 20%
This is the best I've ever rated Geno, and it's due to 1. Square's involvement and 2. Sakurai's acknowledgement/Geno's ballot results probably being pretty good and 3. Geno getting a costume as a result. Before 1 was a huge impediment, while 2 seemed true, it's better to see him explicitly acknowledged as being not just popular here. But nonetheless, he still seems a bit niche.
Geno want: 50%
I'm indifferent. I wasn't a huge fan of the character in SMRPG, and I'm more interested in DK and unrepped series. For third-parties, I'm pretty much on Simon Belmont and Banjo-Kazooie, and if we were getting another Square character I'd prefer a Moogle or a Chrono Trigger rep or something. But I like SMRPG and I don't particularly dislike him either.
Dillon
So this is a game. Not a super popular game, but he has a decent looking design and can be fairly easily adapted to Smash. He got an AT, so he is on Sakurai's radar. But ultimately, I don't think he has enough popularity to be a strong contender. He doesn't come up in the top results of any polls I've seen. Still possible if he catches Sakurai's fancy, but not very likely. Move set wise, though, he might be a little too similar to Sonic, which might be an impediment.
Dillon chances: 4%
Dillon want: 38%
I like his design, but overall I'm not that interested. I find Sonic very annoying as a fighter, so I'd prefer not to have another character in that vein. Presumably Sakurai would try to differentiate him from Sonic though (unless he was a Sonic Echo... *shudder*).