I'd like to see a book focused on either the whole of the Western Heartlands (south of Waterdeep, north of Amn, west of the Stormhorns) or the whole of the Sword Coast (from Luskan or Icewind Dale down to Amn, but only the coastal stuff). To me, that's the most D&D-ish area of FR, but yet the one that has gotten the least detail in supplements. It has traditionally gotten one of the best coverages in the core FR products (after the Dalelands/Cormyr/Moonsea area), but no actual supplements (other than Volo's Guide to the Sword Coast and some city stuff in Forgotten Realms Adventures).
