Does anyone know who will score this game?

You can hear a lovely tune here: http://www.ffta2.com/

Hitoshi Sakimoto. For now, only one music is new (the one on the official website). Otherwise, there are arrangements from FFTA and FFXII.

So Sakimoto might possibly compose a few more tunes but for now only that one tune from the website and rearrangements of FFTA and FF12?  Thanks.  Love the tune on the site.

I'm pretty sure the FFTA and FF12 themes used earlier were placeholders because Sakimoto hadn't gotten to composing any new FFTA2 music at the time.
The full game will probably have mostly new music.

The playable demo available at the Square Enix Party was all Nintendo DS arrangements of the Game Boy Advance soundtrack.  I'm not sure what ratio will be new to old music, but it seems that the Final Fantasy Tactics Advance score will be in full force.

Little update: There's a new tune playing on the FFA2 website now.