The ERJ is not certified for ditching. Not sure how that plays into ETOPS or even what the criteria is to certify an airframe to ditch.
You also have to think about decompression fuel. You have to be able to have a decompression at your worst case scenario (lowest combination of fuel state and distance to a suitable airfield) and be able to fly to an alternate at 10,000 feet. In the military we can waive this if there is enough onboard oxygen to continue flight at altitude, but the dixie cups on the ERJ won't last very long.