It's possible that Marin would be using her harp as her weapon, though I wouldn't be surprised if KT incorporated the Eight Instruments of the Sirens into her moveset in some way.
One idea that I had for her moveset that would be pretty neat would be for her to sing a bit of 'Ballad of the Wind Fish', which would restore health to nearby allies. That'd be pretty cool.
Right now, the only thing I'm banking on with the LA pack is that 'Ballad of the Wind Fish', Tal Tal Heights, and/or the Nightmare boss theme are going to be the remixed tracks if they are included.
As for the characters in the other packs? Linebeck is pretty much a given for the Phantom Hourglass rep. I can see a Phantom (or Phantom Zelda) being a possible rep, given their prominence in both Phantom Hourglass and Spirit Tracks.
For ALBW? I'm going with Ravio and Yuga. I can't see Hilda being a rep, since I have no idea what she would have for a moveset aside from her scepter (and wasn't she an alt for Zelda anyway?). Yuga would be the better choice, given that he would be really unique with his paintbrush and what he can do with it. That, and these games need more villains.