Sawano is so insanely busy these days, there's a chance he might not contribute anything. If Elma's in, we might get some rips from Xenoblade X, but I'm not so sure we'll be getting any new stuff from him, unless his tweets about recent band and vocal recordings for his nZk project are related to Smash in any way. Guess we'll find out.
Recently he's wrapped up work with Attack on Titan S3 which is airing right now. Chances are he'll be recording more music for the show later on for the second half, but we don't know that. He's already completed orchestral work on the Gundam Narrative movie earlier this year, and that will be airing in Japan at the end of the year. It's speculated the "secret project" he was recording at the end of last year was for Gundam Narrative as well. I think right now he's been wrapping up work/mixing on Thunderbolt Fantasy 2 which he's been working on with Takafumi Wada, according to his twitter. That show airs in October. He's doing the OP and ED for that show with T.M. Revolution on vocals, but someone on the Sawano discord says it's not part of the nZk project. We know he's doing a vocal song with Nanami as well for something.
Sawano's Twitter:
https://twitter.com/sawano_nZk (all in Japanese which I can't read well. Lot's of guessing on my part. My pals on the Sawano discord help to figure his current work flow out as well.)
Anyway, we've still got some time till Smash goes gold so I guess it's possible for the Smash team to schedule him for a song or two, if he hasn't done anything for Smash yet. I guess anything can happen till then, but right now I think Sawano is working on vocal songs under his nZk brand and we don't know exactly where those songs are appearing or how/when they'll be released.
Now, to finally answer your question: I'd want him to remix something from Golden Sun. Heeheee! :D