chornedsnorkack, I think a trijet would be very heavy. The APTU envisioned would be a CFM class engine neadly fitting into the tail. It would provide the Ecoliner the required power at take-off with an engine failure while not requiring an engine to developped even larger then the GE90-115, while still providing twin cruise economics.
Henry (
www.kaktusdigital.com) made a very nice animation of the Ecoliner:
http://www.henrylam.net/ecoliner.html
rgds
keesje