What I don't really get is why Geno has such a huge following for Smash Bros., of all things, in the first place.
Ensemble Darkhorses happen all the time. Nintendo has plenty of them. One-shot characters who are entertaining, quirky, charming, maybe they're well-written, maybe they're mysterious, maybe they have a story or character that people really feel or connect with. People want to see more of them, people clamor to have them appear again, they get a cult following.
I'm not surprised that Geno has a fanbase. What I don't get is why so many people are asking him to be in Smash, when hardly any other Nintendo one-shot is getting the same treatment on the same level. Skull Kid seems to come the closest to him in that regard, and even then you can at least say he's had multiple appearances.
Is it only because Sakurai mentioned an interest in the character? Or was there a fair amount of support even before that? I know he had support as far back as Brawl, but I can't remember when it was that Sakurai first showed interest in him.
It's a mixture of things, Geno was a linked to a big meme back when Brawl was being developed; and he became one of the first big fan requests. By the time 4 came out, Geno's fanbase had returned to being extremely small; and there were a ton of characters that were more requested then him, Then Sakurai gave Geno a mii costume and acknowledged his fandom in Smash 4 and recalls that he tried making him playable in Brawl, which led to a huge resurgence in his fanbase.
You have to remember any time when Sakurai states that he tried making a character work, but it didn't work out. It automatically increases the fan demand of that character a ton. Think Takamaru back in Smash 4, not in due to being too unknown, gets a huge popularity boost. But Takamaru's support ended up decreasing a ton from 4 to Ultimate, likely because of the sword.
Anyways now you get to Ultimate, Ridley and K. Rool get confirmed playable early on. This is important because Ridley and K. Rool were seen as "NEVER EVERS" because of how long their fan-demand has been floating. Some of the other big NEVER EVERS like Isaac and Waluigi get AT'd, which for a large amount of the community is a death sentence; meanwhile, Geno is a spirit, which to a lot of people isn't as big a death sentence as being AT'd. So the Geno fanbase gets even larger while the other 2 stagnate. Meanwhile, Banjo gets in and Geno isn't a part of Hero's mii costume pack which feeds into their theory that since Geno is a NEVER EVER that he'll be playable too. A huge portion of the Geno fanbase becomes really vocal, which makes them really divisive in other communities, so now you have haters increasing the amount of Geno discussion dramatically.
Now you get into the second half of last year, one guy leaks all the costumes in BK's line (except Sans) and lists Mallow and Smithy (but not Geno) as upcoming costumes. Then, at the end of October we get the Cacomallow leak; which most modders aren't able to definitively disprove and as time went on, interest on the leak died out (you can't prove it, you can't disprove it) and most people thought that it's not real. But then, a ton of Geno fans think the leak is still real due to the quality and the fact that it lined up with the Mii costume leak. It's been 2 fighters since then, with a 3rd one coming up really shortly. On top of this, thanks to Cacomallow most fans think that Geno is going to be revealed "soon" due to the costumes. So thanks to all of this, the Geno fandom has been on high alert looking for Geno in any way they can because he's DEFINITELY happening. The more likely a fanbase thinks a character is, the more hate they'll end up getting especially if they're incredibly vocal about it.
Now the problem is that at least in DLC, fanbases don't become super vocal and practically act like they're in unless there is some huge proof that a character is coming relatively soon, which minimizes the amount of controversy/hate a characters fanbase generates. For most characters this is like a week or 2 at most. However, the Geno fanbase has been super vocal about how likely Geno is for almost an entire year, which a lot of people don't take kindly to, which generates more discussion around the character. A good chunk of the DQ fandom got hate on other sites because they acted like they're practically in for 6 months and Hero was a highly controversial character upon reveal on sites like reddit. This is amplified for Geno, because unlike DQ which is a massive franchise that most people think warrants some sort of representation, Geno as a character is incredibly small in the grand scheme of things and is only seen as a huge character to his fanbase.
TL;DR: The reason why Geno is so massively discussed is because he has: some genuine fan support going as far back as Brawl + some new fan support from after Sakurai gave him a mii costume + a natural NEVER EVER multiplier + how vocal his fanbase is compared to their size + how many leaks surround the character since the start of Ultimate + the bandwagon effect (a good chunk of people want this character, so should I) + the pity effect (this character has been asked for since Brawl, I feel bad for his fans) + how much hate Geno/his fanbase gets. There are definitely bigger requests then Geno, but they aren't as divisive which is why you see them discussed far less. Unironically speaking, the divisive reputation Geno has garnered within the last year have boosted his discussion to the point where it's out of proportion to his popularity.
