Xenoblade's OST to me was a handful of great songs mixed with a ton of mediocre ones. Almost all of disc 2 was very boring to me. At least the last song was good. Most of the stuff works better in-game than on its own, but overall it wasn't an OST I cherished very much.
Sawano's management company. They have a number of different composers and musicians under their belt such as Yuki Hayashi, MPI, Takafumi Wada, Asami Tachibana etc. They mostly work on live action Japanese dramas and movies.
They've been starting to work on anime more often recently. No doubt due to Sawano's uprise in popularity after working on shows like Gundam Unicorn and Attack on Titan.
Sawano is working together with Wada, Tachibana, and Legendoor's newest recruit, Megumi Shiraishi, on the upcoming Wit Studio (Attack on Titan) anime called Seraph of the End.
Links:
http://kisetsu-no-uta.com/related-artists/composers/ (in English. Info is a bit outdated.)
http://www.legendoor.com/ (in Japanese. Up to date, of course. You can see what all these composers have worked on from here)
If Sawano isn't composing Xenoblade X by himself, I would expect these people to be the ones he'd collaborate with. But who knows. We'll find out soon enough.