>If I designed such a system from scratch, "remaining fuel" would be part of my telemetry.

Careful what you wish for. I'd rather people skip the queue by pretending to be low on fuel than people skip the queue by actually being low on fuel.

You mean that ATC would abuse their position by making planes circle as long as they have some fuel left?

No I mean people would take off with less fuel so that by the time they reach their destination they could skip the queue

This is provable, though (there are regulations that say how much fuel you must have at takeoff - enough to divert comfortably to a suitable airport + some reserve for circling), and could be heavily punished. Up to the withdrawal of necessary licences.