No, 2B doesn't have a decade of fan support behind her, but she's got recency bias and a wider appeal than Geno (even though this thread likes to pretend otherwise when she gets brought up, but they did the same for Dragon Quest, so yeah...). Also, characters that appear in other crossover fighting games that don't appear in others is just kind of dumb to bring up given that these aren't really active decisions that decide which characters appear where and more specifically that Bandai Namco develops Soulcalibur and also develop Smash, so I don't think it'd even be an issue worth bringing up.
2B is hot and popular right now, so that's one reason to look to capitalize off of her. But beyond that, Drakengard/Nier is a longer running series that is beloved by a number of people and recently broke big, so that's another reason to include her. Similarly, Yako Taro is another auteur Japanese developer that speaks to the very idea of Sakurai's "representations of Japanese gaming" and one he specifically respects a great deal. Nier will continue, so Square Enix is certainly interested in seeing the brand continue, so I don't see any real argument against her. She's actually pretty damn likely when you look at it. Yeah, there are other choices, but Square Enix, Nintendo, Sakurai, and Yako Taro all gain from her inclusion. Sora's not even Square Enix's to license out, so that's really not worth bringing up. Lara Croft is an acquisition and not an originally Japanese character, which may hurt her given Sakurai's general focus on Japanese gaming in Smash. Crono is just a crazy hail mary of an idea because Chrono as a series is largely going to remain dead due to various issues and I don't think there's much to compel them to "want Crono over 2B." And Akira Howard? Astral Chain didn't immediately light up the charts based upon sales data, and we'll see what they want to do with them. They certainly don't seem to have made the same impact that 2B and Nier Automata did though.
And, no, we don't have anything from insiders. Fatman has proven to me he's not really worth listening to, Sabi burned all of her good will in the past few weeks (particularly with the whole transphobic mess and accusing another "leaker" of trolling or whatever), Vergeben doesn't seem to know anything at all (and hasn't really offered anything new since Dragon Quest), and an unidentified leak that nobody really knows the proper source of came out with a Mii costume list. There's no solid leak about **** and we're all just as in the dark. The insiders aren't actually backing much of anything right now to be honest, they're mostly just taking seemingly random shots in the dark and not vocalizing any "leaks."