Man, I'd kill several thousand traitorous Bolsheviks for a new Icewind Dale, but that was made by the team at Black Isle, with the oversight of Interplay, on Bioware's excellent engine, with the collaboration of TSR. I beg to differ that the "focus" of Obsidian's other games were the choices and plots. There were many, many combat sections. Sure, the characters and so on were the best parts, but that does not mean that Obsidian didn't pour a lot of time into fighting stuff.
Dungeon Siege isn't a branching out, where they're trying their combat legs. If they wanted to do that, they'd pick up a license for an action game or something. The DS games were essentially an automated and boring version of a Diablo-like system.
Obsidian has a real chance to fill a niche that hasn't seen action in a long time. They are obviously selling units - three licensed games based on popular franchises (going on four) plus an original backed by Sega. Given those game's obvious strong and weak points, there's a reason people are buying them. The niche, obviously, is for choice driven narratives with interesting characters and real consequences to your actions. I wonder if we're going to get more than the generic corporate talking points about why Obsidian chose to agree to Dungeon Siege, why Square chose the game and why they chose Obsidian, and how Obsidian is overcoming the difficulties they've had with combat in the past.
Then again, maybe this turns out to be a Planescape Torment with light hacky combat. It's not like we would lose any great mythology or classic gameplay or anything like what happened with Fallout. And, after all, Square and Obsidian are companies that have always prized story over gameplay. However, that's probably unlikely just given the fact that this still is an existing license.