The problems I see with this are:

1) The IT side of it would not be insignificant in implementing this; and
2) This will basically ruin the existing revenue management models the airline has.

For the amount of the fee, it just doesn't seem like it would be worth it ...

The one potential advantage I see to this is that it can only be purchased on tickets bought directly from the airline, though with commissions to travel agencies and booking sites already non-existent, I'm not sure how much of an advantage that is.