If all of the polite asking goes nowhere, to what extent could the FA (or GA or whoever) force someone in the exit row to move? Does the COC guarantee a passenger the "right" to their specific reserved seat? I would think that QX has the right to move passengers around.
It seems odd that QX would rather force someone off the plane and have a seat go empty than inconvenience an exit row passenger (maybe even anger them) but get the revenue. While being tall is not legally a handicap, it sounds, from the stories told above, that it's a handicap in some situations - accommodating them in an exit or bulkhead row doesn't seem unreasonable to me.