Actually hold on I think it could actually be Agnes lmao.
1. Vergeben doesn't want to say who the character is. If it's Agnes, who is honestly one of the biggest jokes in the community after the Agnes leak, Vergeben saying it's actually Agnes would cause a great deal of ire towards himself because the community is angry it isn't Geno because why would it, instead, be this laughing stock of the speculation community? It's leaker suicide for Vergeben to say it's Agnes because it immediately leads people to doubt what he's saying due to association with the Agnes leak.
2. Other options Sakurai considered (not planned) for Cloud's spot was Onion Knight, who had a class changing gimmick. He even said "that might work" after saying the idea. And this time, we get a real character rather than an avatar like Onion Knight.
3. Sakurai's Nintendo Dream interview about Bayonetta mentions that being Nintendo exclusive makes negotiations easier (it's on Source Gaming, part 2). Both Bravely games are exclusives, and Square has talked about a third one coming sometime (presumably after KH3 is done and FF7 remake is underway). This is probably why Bayo comes from Bayo 2 on the website, because that's the exclusive game.
4. Speaking of Bayonetta, the Bayonetta and Bravely Default actually have a lot of commonalities. They are nicher franchises coming from their producers, so they don't compare well with the legendary lineup we have in Smash. As you all know, Nintendo publishing Bayonetta 2 was the only way the game could get published. But did you also know that the only way Bravely Second would've released internationally is if Nintendo published it as well? Nintendo has a vested interest in this series and sees the potential no one else does.
5. Bravely Default hype was at its peak during the 2013-2016 period when the games were being released. Internationally, the first game was released in 2014 and the second was released in Japan in early 2015. These are crucial dates because the ballot started at this time. And you know what other game released around this time? Bayonetta 2. I'm not suggesting that Agnes tops the popularity polls because I'm convinced she doesn't. But we don't know what the actual ballot results looked. I know things suggested Bayo may not have been the ballot character due to being planned after two weeks, but it's still feasible she did well, especially at first when led Sakurai to go with her.
Now it wouldn't have to be Agnes and could be anyone in the cast, but I think she's probably the pick due to being the most important in the first game due to her prominence on the boxart. Given that the concept is class switching rather than innate abilities, it's possible that they pull an Alph and have Agnes, Ringabel, Tiz and Edea each with two costumes.