The Mii Costume not appearing yet doesn't means much, we can use that logic and say that Chocobo is also coming because its Costume still didn't come back. And Geno's can still perfectly appear later, instead of adding back Jackie's and Akira's costumes alongside Joker, a Sega character, they came back alongside Terry, a SNK character, so Geno's Mii Costume can come back with another character.
Sure, but considering what we've heard from the Mii Costume list and the CacoMallow post, it seems likely we're getting another SquareEnix costume alongside the Geno Costume and the Chocobo Hat, most likely a Mallow Hat, so where do these all come back? Returning Mii Costumes thus far have come back in groups of twos: Tails & Knuckles, Proto Man & Zero, Jacky & Akira. If we look at the remaining costumes that have yet to return, they for the most part go together in groupes of 2: Mega Man X & Mega Man.EXE, Hunter & Rathalos, and Geno & Chococo. The only exception to this being the Namco costumes with Lloyd, Heihachi & Gil. If it were only the Geno Costume and Chocobo Hat coming back then sure, it's possible that they could come back whenever, but with it being rumored that we're getting at least one more to go alongside them, then that seems significantly less likely.
So far, the limit for how many Mii Costumes we can get with any given fighter appears to be 6. The least we've ever seen a fighter get in terms of costumes from their own series is 3, not counting Banjo who is an obvious outlier in all this. The most we've ever seen a fighter get in terms of unrelated costumes, ie. costumes that don't come from their series or company, is 2. Since we've yet to get more than 6 costume with any one fighter and we've yet to get more than 2 unrelated costumes with any one fighter, it seems that 2 would be the limit for unrelated costumes.
I think that 2 is the cut-off point because so far we've never had more unrelated costumes included with a fighter than related ones, like more Sonic costumes than Persona costumes for example. So if there are to be 3 costumes coming, then that would either mean that these costumes will be coming with a character from their series/company, or one of the costumes would be upgraded to a playable fighter and something would be included in it's place alongside the 2 remaining costumes.
Let's use the Namco costumes as an example. If these costumes are to return, they'd either have to be packaged alongside a new Namco fighter, or one of these costumes would have to be upgraded to fighter status, which would mean that they would come with their own new costumes for a complete package:
Namco Fighter: 1-3 costumes from their own series, the 3 returning Namco costumes, and 1-2 unrelated costumes assuming there's room for it.
Lloyd or Heihachi get upgraded: 1-3 costume from their own series, the 2 returning Namco costumes, and 1-2 unrelated costumes assuming there's room for it.
Going back to the SquareEnix costumes, if we are to get 3 of them and Geno isn't the fighter, then that would mean that whichever fighter they're coming with has to be from SquareEnix. This would look something like this:
SquareEnix Fighter: 1-3 costumes from their own series, the new Mallow Hat, and the returning Geno Costume and Chocobo Hat from Smash 4.
Another Final Fantasy Fighter: 1-2 new Final Fantasy costumes/hats, the returning Chocobo Hat, and the returning Geno Costume and new Mallow Hat.
But of course, the Mii Fighter list also mentions a Smithy costume/hat to go along with this, which would seriously tip the scales in favor of Geno becoming a fighter. If the list of known SquareEnix costumes grows to 4, with three of those costumes being from Super Mario RPG, then the fighter couldn't be just any old fighter or even an unrelated SquareEnix character, since there would be an unprecedented imbalance in the number of Super Mario RPG costumes compared to whoever was coming, it would either have to either be Geno or someone from Super Mario RPG, most likely Geno. So basically like this:
Geno as Fighter, A Scenario: Mallow Hat, Smithy Costume/Hat, Chocobo Hat, 1-2 unrelated costumes.
Geno as Fighter, B Scenario: Geno Costume, Mallow Hat, Smithy Costume/Hat, Chocobo Hat, 0-1 unrelated costumes.
An unlikely SMRPG character who isn't Geno: Geno Costume, Mallow Hat, Smithy Costume/Hat, Chocobo Hat, 0-1 unrelated costumes.