chornedsnorkack, i once specified an aircraft like you mention : the A320 enhanced performance with a lenght inbetween 320 and 321, new engines, interior and roof top windows
It could offer a bit more range & less capasity the the A321 without real dramatic modifications. Henry Lam (kaktusdigital.com) did a IMO great visual on it:
However IMO it wouldn't really offer the payload range operational flexibility to be a 757 / 767 / A310 successor..