An arrival slot swapping arrangement within an airline is a novel idea that could well have benefits from time to time for the major users of an airport. However any arrangement that favours the aircraft that turns up at the holding pattern with the least amount of fuel is a terrible idea.
A considered crew puts on extra gas, accepts the payload penalty, wears the added fuel burn but then cops a delay as another operator jumps the queue as they didn't bother to put the fuel on. Can't see that plan working.