I think it means absolutely nothing for the roster - with the exception of the Metal Gear Solid composer and Xenoblade composer.
Brawl generally tried it's best to get the original composers of tracks to remix them for the game, and it seems like this game is no different. While I don't think this means anything for all of the composers (as in, having the composer from Final Fantasy XIII doesn't really mean I will see any Final Fantasy XIII tracks - FFXIII's soundtrack made great use of the violin and piano, so I'm sure any songs with them will have Masashi Hamauzu involved - that violin rendition of the Smash 4 theme that we've heard play at the end of Smash Run rounds, as well as when Sakurai walked on-stage during the Invitational, sounds like something Hamauzu would put together, and I love it), I think it MIGHT mean something for Snake since, well, he's a veteran. I think it would be weird to not have him in the game, knowing that the composer worked on songs for him in Brawl, but isn't doing so here. Either way, I'm really curious to hear what they'll have.
And it might bode well for a Xenoblade character, especially since multiple composers from that specific game are here. Now I know that various TEKKEN composers are there too, but I don't really look at that the same since they work under Bandai Namco, who are developing the game anyway. It's no surprise that TEKKEN and Soul Caliber composers would be working on this even though there probably won't be characters from those games.