[_tqr3]

Sounds like logistical nightmare.

How do you keep track of bin space while accounting for variable luggage sizes and compliance?

[josephcsible]

Put physical dividers in the overhead bins so that oversize luggage won't fit at all and has to be gate-checked.

[_tqr3]

The main disadvantages are that physical dividers add weight and require maintenance. Also, they reduce flexibility, preventing the ability to tetris more bags into a bin.