I think Larian's style lends itself to a deep dive into a relatively small geographic area. I voted for Ravenloft; I'd love to see Planescape or Spelljammer, but I think that could be left to another studio. My dream assignment for Larian would be Monte Cook's Ptolus. Everything happens in a single city with layers upon layers of intrigue. It's so good and I think Larian could really do it justice.