I'd like to take the time to point out the last paragraph on the music page:
We've asked our group of arrangement supervisors to listen to an elite selection of Nintendo music and asked them to arrange several of their favorite songs...which means there will be quite a number of songs.
So the only thing they're even
doing is helping with the music. There's no guarantee that the list of composers has anything to do with what third parties are involved with the game, and the fact that Masahiro Sakurai (the game's director and the man who writes this blog) said some time ago that there would only be two or three more third party characters past Snake means extraneous characters are very very unlikely. If any of those group resources show up in any form, it'll either be stages (also unlikely) or a ridiculous number of new trophies (the most feasible idea). But likely, they won't appear at all.
Another reason for the above is the fact that many of those composers did a lot of things other than what they're credited for; one reason they're credited for what they are on that page may simply be so you can recognize them easier if you don't pay attention to composer names in video games. For example:
- Minako Hamano, who is credited for Metroid Fusion alone, also helped Kenji Yamamoto with Super Metroid and Zero Mission. She did Brain Age's OST with Akito Nakatsuka.
- Motoi Sakuraba, credited for Golden Sun and and Mario Golf/Tennis, also did Star Ocean, Valkyrie Profile, and Baten Kaitos. He is, however,
far more well-known around the video game music loving crowd for his work on the Tales series than anything else.
- Ryoji Yoshi tomi (last name separated due to the curse filter) is credited for the Wario Ware series, but also did the OST for Metroid II back in the day.
- Yoko Shimomura, credited for Kingdom Hearts, also did the music for Super Mario RPG and the Mario & Luigi series, Breath of Fire, Parasite Eve, and any of the Mana games that Hiroki Kikuta didn't do. One of her most famous soundtracks was Street Fighter 2, alongside Alph Lyra.
So yeah. The rumors due to this page are going a bit overboard. With all the games all these people worked on, you could start trying to throw 50 bajillion third party characters in, which isn't going to happen.