Sounds like there may be a playable demo coming for Dead Space Extraction. A hint was dropped from EA's Dead Space Twitter account, isaacclarke: "Did walkthroughs on 3 Chapters in the game. We also reviewed our super secret special Demo build......guess it's not to secret anymore....".
issacclarke also revealed that the Wii game will likely get an "M" (for Mature) rating. It would be hard for a horror game series like Dead Space to get anything under an M rating. Nothing has been formally announced, but hopefully Dead Space Extraction will be getting a downloadable demo channel like Metroid Prime Corruption had. But then again, with an "M" rating, maybe the demo will be provided on disc with pre-orders? Hopefully we'll hear more soon. For now, it's wishful thinking (rumor).