BA used to have some limited ability to prioritise amongst our own flights when holding became excessive. We used to tell our own ops what our fuel endurance before diversion was if given lengthy holding delays. BA would then liaise with ATC allowing aircraft with less endurance to perhaps land at destination rather than divert. This system was not used to put premium pax first but to allow aircraft with less fuel a greater chance of landing by swapping their place in the queue with another company aircraft with more holding time available.