I think it could be Geno, but this is a poor argument that it could be him.
TGA audience, heck even most of Smash's audience, does not participate in fan polls. Most people who play the game and buy the DLC don't look up sourcegaming, or even spend their time here speculating; because frankly 80% of Smash's audience is probably pretty casual and care not about anything except the newest popular titles. It goes a long way to show that in a game that sells 20 million, a poll with 5000 votes is considered a good sample size; even though it's prone to a lot of biases, such as ease of recall and availability bias (something that can be easily recalled makes it look more probable). That's the reason why certain characters votes in polls skyrocket if there are decent rumors surrounding them (for example, 4 out of the 5 top 5 in Sourcegaming's poll all had decent rumors backing them up, and all of them featured 2-3x the increase compared to their results from last year). And in fan polls, let's be honest a lot of people vote for characters that they want AND they think are likely.
Joker barely had any rumors surrounding his possible inclusion in Smash, and considering that P5 was playstation exclusive; most people barely gave him the time of day when discussing his chances. Yet, he was definitely among the most well received characters; especially considering the reaction of the game awards audience. Byleth had most of the rumors surrounding him dismissed, considering the huge controversy FE has within the community; not to mention most FE fans didn't really think they'd dip into an FE character either.
That said, what both of them did have was the fact that their games are pretty new, popular, and familiar to the audience that watches the game awards. Geno isn't a new, popular, trending character; he's popular within the Smash audience, but let's be honest he's objectively far more obscure compared to the likes of Byleth and Joker when they would've gotten in.
He could still happen though, as we don't really have any specific long lasting pattern with TGA announcements; though I wouldn't say it's particularly likely.