He denies speculation the game is a prequel to Mass Effect 2, saying, "[The game] is not a 'bridging' story between Mass Effect 1 and Mass Effect 2. It is a cool little side-story about one of the upcoming Mass Effect 2 characters. It is not 'required reading' to enjoy the core trilogy, but if (sic) a fun optional 'extra' game."
Among other details revealed in the post is the fact that Jacob's Story is "being done by a separate, dedicated team with no connection to any Mass Effect DLC development or patches," stressing it's not the reason there hasn't been any more Mass Effect add-on content since the release of Bring Down the Sky. Finally, Priestly notes that "BioWare and the Mass Effect team want to branch out in a number of ways with the ME universe, and this is just one example of such branching out." More details on the title are said to be inbound "later this month." (That'd be late May for those disoriented by the end-of-week month change.)