Ubisoft have announced the launch date of the expansion on their new official site: February 28th, 2013. The title, "Shades of Darkness" is a match to my own suggestion, a variation of the existing game from the Quest for Glory series.

The expansion will (as we knew) be a "stand-alone" version, and feature (as we also knew) the hero Raelag leading the Dungeon faction. A "complete edition" will also be made available:

"... containing the enhanced game, all bonus maps & items, adventure packs, the original soundtrack of the game and the Shades of Darkness expansion, set for release on PC on the same day.

Is there a real difference betwee the two except for the DLCs, who knows, but this certainly points to the likely fact that there will be one expansion only.