Don't expect the V8 to be replaced so soon. The Coyote engine is only 3years old. The ecoboost will most likely be a 3rd powerplant. Unless it is significantly cheaper or a lot better on gas ( which doesn't seem to be the case in current ecoboost models ) why the hell would you go with a turbo 3.5L instead of a N/A V8 which has much more potential to mod for power?
Yes it will be slightly lighter in the front with the 3.5L and it will be exciting to see but only as a 3rd option or if it replaces the V6.