My expectation is that this is a new NWN3 game. Who the develeoper will be is unknown. BioWare is now part of EA and will not deal with Atari in any fashion -- let alone get involved in a game where they do not own or control the IP. That ship has sailed.
As for Obsidian, given the poor performance of Alpha Protocol and the cancellation by Sega of their Aliens/Marines RPG last year, I would not be surprised if Obsidian Entertainment is involved again.
Frankly, I'm somewhat surprised to see a PC CRPG for D&D again. There are exceedingly few PC only titles these days. The fact that there were no electronic exhibitors at Gencon 2010 is not an accident folks. That ship has also for the most part, regrettably, sailed. The money is just not there anymore when compared to the far more profitable platform that 360 and PS3 console games provide. (MMOs excepted).
As for the setting... look: the cost of any setting from the developer's viewpoint is exactly the same on a royalty basis. Given that, a developer will choose the one with the most traction with the average computer game buyer. And that setting is most assuredly the Forgotten Realms, leveraging either the Neverwinter or Baldur's Gate brand names. In this case, the Neverwinter brand seems to be the next batter up given the recent IP domain name reservations.
The rumor of a NWN Forgotten Realms MMO has been around for quite a while. It would not surprise me to learn that this was a MMO game. DDO has been a commercial and economic failure for WotC, Atari and -- for the most part -- Turbine. (There is no debate about this point. You might like the game, but I'm counting $$, not smiles and good feelings.)
Were I Feargus and Co at Obsidian -- my first choice would be to return "Neverwinter Nights" to its original "MMO roots" [insert pointless and miguided nostalgia over AOL's Gold Box engine NWN game here]. Because the copy protection for a MMO is guaranteed they are for more profitable if you succeed. They also cost a helluva lot of money to develop properly, too.
As for the mod tools and any DM client for NWN 3... that ship has also, regrettably, sailed. The tile based game that was NWN1 encouraged modding in a manner that was an odd convergence of widespread gaming PCs, the internet, and technical art requirements that were within the capability of enthusiasts.
By the time NWN2 was released, the technological curve had progressed to the point where all but the most hardcore of enthusiasts had been effectively shut out of participation. The days of the solo modder ended. And I assure you, even a team approach is exceptionally difficult to do.
And yes, for those of you who recorgnize the handle, I was the leader of DLA team that BioWare hired to create the third expansion for NWN1, Wyvern Crown of Cormyr.
So I do lay claim to extensive knowledge in this area. The plain fact is that the 3d art tools now involved in the creation of a modern CRPG are beyond the skillset of all but a dozen or two members of the game community. The difficulty in producing much of anything for use with Dragon Age's toolset and engine is clear evidence that a toolset designed for community use is just no longer worth it, imo. (And for the record, BioWare paid a lot of money to fly ex-members of DLA and other NWN1 community members to Edmonton for training on the Dragon Age toolset, too. They really did try to make it happen for Dragon Age.)
Sad, but there it is.