This is one of the least likely games ever conceived, no doubt. There's an
interview with the Bioware folks at Wired. It may not be worthy of a new thread, but since the only other Sonic RPG thread is in TalkBack, I figured someone may as well create a proper discussion thread for it here. This interview is perhaps most interesting because it sounds like they interviewed a talking press release.
The basic gist of it is that they were already big Sonic and DS fans, so they "jumped at the chance" to work on this game. The game is a "fast-paced, story-driven experience with tons of exploration, customization and progression," and "You’ll see
all the popular characters and story elements that Sonic fans love." (emphasis added).
It sounds to me like it hasn't moved off the paper yet.