A few years ago, rumor also had it that a third installment in the series was being created at Black Isle Studios. The studio was closed since then and its founders moved away and united again under the Obsidian umbrella.
Therefore, Obsidian may be the mysterius developer of choice, especially since the company has taken care of two sequels spawned initially at BioWare: Neverwinder Nights 2 and Knights of the Old Republic 2.
Speculation will go on wildly for the time being, as none of the parties involved wish to comment on the matter. Still, do keep you fingers crossed.
The last good title in the series was released back in 2001: Baldur’s Gate II:Throne of Bhaal