A lot of professional comment on PPrune suggests the existing 739 is a stretch to far and can barely get airborne with a full load at some places and usually requires a longgggg runway for a short haul aircraft.
It is too narrow for the modern world and many parts of it must be same as the 50+ year old original . Yet another stretch is really going to make it a 'Triggers Broom' (for non Brits, thats a ten year old broom thats had five new heads and four new handles)