Two points to add to the mix...
Before I retired as a 747 Capt at LHR I noted how much holding I did before landing over a year. It came to just over 10 hours - 10 to 15mins on average 5 times a month for 10 and half months.
That's the best part of 120,000 litres of Jet A and Jet A1 burnt by this one Pilot in a year - that's out of 21 years at LHR. Take a look at FR24 some mornings and have a guess how much fuel is being wasted at the holding stacks......
And another thing..........
Failure to meet pollution targets at ground level is predicted on surface traffic usage - cars, buses and trucks. By the time this development is up and running the shift to electric, hybrid and hydrogen will render those forecasts meaningless.