As has been pointed out in these forums in the past, both 13.3" and 11.6" models of the MacBook Airs has/had thick bezels.
If it was possible to reduce the size of the bezels without changing the width and length (chassis) of the unreleased MacBook Airs - allowing the screen size to increase to 13.8" - 14.0" but still fit in the "standard" manila envelope - would there be an issue with that?
That is a different thing altogether. However, currently bezels are thin (within a few mm), any gains would just be negligible.