Well, here's what I think. I'm going back to Super Mario 64 DS, where they pretty much used the same MDID sequence and synthesizer. However, knowing that this is a new platform built on it's graphical power, I believe they're going to perhaps update the synthesizer a bit in order to make it add on to the overhaul of the game.
A.K.A. They're going to have the same music, but they might get instruments better than the N64 version. My only issue, however, is that doing so could potentially ruin the nostalgic effect.
Video of gameplay shown at public demos have so far confirmed that the music and sound effects are exactly the ones used in the N64 version. Now, maybe these are just placeholders for a revamped soundtrack, but I doubt this will be the case. The soundtrack and effects actually hold up quite well, and given the fact that it's on a handheld as opposed to being put through fancy 5.1 surround sound systems I think the fact that they are 10+ years old is just something to be forgiven. If you listen to previous handheld Zelda music of late (PH, ST) it's around the same quality as OoT's original themes.
I for one would love to hear fully orchestrated music provided, but I know it's just a pipe dream for a 1st party Nintendo handheld game at this time.
Anyway... I do not believe that it will have a new soundtrack. The music will most likely be the same. However, there is a chance that there will be a new cover of the music, but as basement24 said, the demos use the original sounds. So, unless the developers just stuck the original music in at the demo as a placeholder, there won't be a new soundtrack.
God, I wish for both original and re-orchestrated music. :O
Maybe the'll actually have the option to use either or (assuming all the stuff is remastered).
The only thing I don't want changed is the Song of Storms, because that annoying nintendo 64 music quality actually makes it what it is. P: