I haven't experimented with all Arcade difficulties yet, but as far as I understand, the new rules are the following:I don't think arcade has been as randomized as we had thought. Every round through Normal difficulty I've done, she's always been the 8th match.
1). Stage order is set in stone across the board on all difficulties.
2). Legendary difficulty is completely set in stone with the order of opponents, no randomness whatsoever.
3). Bosses are set in stone (for example, Very Hard final boss is still Azwel no matter what).
4). Cursed Moonlit Woods stage is currently completely occupied by Amy. Combine it with the fact that stage order is set in stone across the board and it basically means one can always predict where Amy will show up in the Arcade. I believe this last rule is temporary due to Amy being a new character Bamco really want to show off. I expect Cursed Moonlit Woods stage to produce random encounters instead of Amy after a future patch or two. I'm pretty sure that will happen at least by the time Cassandra is released (also by that time I expect Cassandra to completely occupy Shrine of Eurydice: Cloud Sanctuary stage in return).
Snow and Mitsurugi also make sense since both Setsuka and Mitsurugi use Japanese martial arts with Iaido techniques (both sheathe/quickly unsheathe their swords mid fight a lot as a part of their fighting styles).They left in files which define all the various properties of a character (meshes, size, gender, fighting style, etc). But no one has reverse engineered for the format of these. I can tell based on strings in the files that they're currently using assets of other characters. Which are the following:
Yell is based on 0x0C (Kilik)
Stone is based on 0x0C (Kilik)
Reptile is based on 0x0C (Kilik)
Yellow is based on 0x0D (Xianghua)
Star is based on 0x0F (Yoshimitsu)
Snow is based on 0x01 (Mitsurugi)
I'm not sure if there's much meaning to get from this. Yellow being Xianghua could maybe be a hint that Yellow is in indeed Hwang since they had similar movesets back in SC1. Yell is currently Kilik because of his staff and Hilde has a long weapon? That's kind of far fetched. If Stone and Reptile are Rock and Lizardman, then it makes no sense they'd use Kilik as placeholder.
But well, these could just be arbitrary placeholders with little meaning.