There's a reasonable chance that the next Baldur's Gate game will be announced next week. The official Baldur's Gate website, which has been used to promote the Enhanced Editions of both Baldur's Gate and its sequel, now features a countdown timer that's ticking down to the reveal of what appears to be the next game in the series.
Developed by Beamdog, which handled the Enhanced Editions of the BG series rather than BioWare, the next game in the series is expected to take place between the events of the first game and the second game. It won't be Baldur's Gate III, but it'll be much more extensive than anything the developer's ever worked on before.
The game has currently been given the project title of Adventure Y and runs on the ancient, but still sturdy Infinity Engine. It's expected to touch upon the Bhaalspawn storyline that the original two games are based on.