-discover the past between Luc and Sasarai
That's pretty much already been dealt with...
As for me:
-Discover the mystery of the Sindar in length for once
-Visit Nagarea/Kanakan/Western continent
-Unveil more of the True Runes (don't know if they'll get to show all but III revealed the most)
-Find out about Jeane/Zerase/Eresh/Viki/Little Viki (unless Konami is mean and wants fans to speculate forever)
-Deal with Harmonia, the Hikusaak, and his plan.